An excellent paper on the history of the word scientist has been published back in April 1964 (http://dx.doi.org/10.1080/00033796200202722). Here are some excerpts as well as further comments, that I consider particularly relevant to a range of discussions taking place nowadays:
"[...] To the historian of science the present story is significant because it marks in a dramatic way the transition of the cultivation of science from the hands of the amateur to those of the professional. The designation scientist, with its overtones of specialism and professionalism (cf. dentist, pediatrist, etc.) was not in accord with the persona that the gifted amateur had of himself and his scientific pursuits; his ideal was that of a man liberally educated, whose avocation was science as an intellectual cum philanthropic recreation, to which he might indeed devote most of his time without ever surrendering his claim to be a private gentleman of wide culture. In particular, to be thought of as pursuing science for money was distasteful. Even men like Davy and Faraday, who actually earned their livelihoods by the practice of science, were so imbued by this attitude as to reject opportunities of enriching themselves by patenting or otherwise restricting the publication of their inventions. The genuine amateurs and the actual professionals, who still maintained the same ideals as the amateurs, chose science for its own sake and regarded themselves as benefactors of mankind; they scorned
To heap the shrine of luxury and pride
With incense kindled at the Muse's flame.
They did in fact use similar lofty expressions in describing their ideals. To them the word scientist implied making a business of science; it degraded their labours of love to a drudgery for profits or salary.
The old ideals died hard, but they could not survive the educational reforms that placed technical education on the same footing as education for the learned professions of medicine, law, and theology. To the student preparing for a career, science was now presented merely as another alternative profession; and the word scientist carried no less desirable connotations than did physician, lawyer, or clergyman."
The term scientist was coined by the English polymath, Anglican priest, philosopher, theologian, and historian of science William Whewell (master of Trinity College, Cambridge) in 1833. It was first published in Whewell's anonymous review of Mary Somerville's book On the Connexion of the Physical Sciences, which appeared in the Quarterly Review in 1834:
"The tendency of the sciences has long been an increasing proclivity of separation and dismemberment... The mathematician turns away from the chemist; the chemist from the naturalist; the mathematician, left to himself, divides himself into a pure mathematician and a mixed mathematician, who soon part company; the chemist is perhaps a chemist of electro-chemistry; if so, he leaves common chemical analysis to others; between the mathematician and the chemist is to be interpolated a 'physicien' (we have no English name for him), who studies heat, moisture, and the like. And thus science, even mere physical science, loses all traces of unity. A curious illustration of this result may be observed in the want of any name by which we can designate the students of the knowledge of the material world collectively. We are informed that this difficulty was felt very oppressively by the members of the British Association for the Advancement of Science, at their meetings at York, Oxford, and Cambridge, in the last three summers. There was no general term by which these gentlemen could describe themselves with reference to their pursuits. Philosophers was felt to be too wide and too lofty a term, and was very properly forbidden them by Mr. Coleridge, both in his capacity of philologer and metaphysician; savans was rather assuming, besides being French instead of English; some ingenious gentleman [Whewell himself] proposed that, by analogy with artist, they might form scientist, and added that there could be no scruple in making free with this termination when we have such words as sciolist, economist, and atheist -- but this was not generally palatable; others attempted to translate the term by which the members of similar associations in Germany have described themselves, but it was not found easy to discover an English equivalent for natur-forscher. The process of examination which it implies might suggest such undignified compounds as nature-poker*, or nature-peeper, for these naturae curiosi; but these were indignantly rejected."
* When the German association met at Berlin, a caricature was circulated there, representing the 'collective wisdom' employed in the discussion of their mid-day meal with extraordinary zeal of mastication, and dexterity in the use of the requisite implements, to which was affixed the legend -- 'Wie die natur-forscher natur-forsehen' which we venture to translate 'the poking of the nature-pokers' [Whewell's note].
As Sydney Ross notes, proposed in this way, especially with the detractive association of sciolist and atheist thrown in for a humorous effect, the suggestion was obviously frivolous and could not have been considered seriously for a moment. Six years later, in his Philosophy of the Inductive Sciences, Whewell made the suggestion again, this time more soberly, in the following passage:
"The terminations ize (rather than ise), ism, and ist, are applied to words of all origins: thus we have to pulverize, to colonize, Witticism, Heathenism, Journalist, Tobacconist. Hence we may make such words when they are wanted. As we cannot use physician for a cultivator of physics, I have called him a Physicist. We need very much a name to describe a cultivator of science in general. I should incline to call him a Scientist. Thus we might say, that as an Artist is a Musician, Painter, or Poet, a Scientist is a Mathematician, Physicist, or Naturalist."
Neither term gained wide acceptance until decades later; scientist became a common term only in the late 19th century in the United States and around the turn of the 20th century in Great Britain. For instance, Faraday never used the words scientist or physicist, describing himself as an experimental philosopher to the end of his career. Lord Kelvin, when his attention was drawn to physicist some fifty years later, also disapproved. He preferred naturalist, which he found defined in Johnson's Dictionary (1755) as 'a person well versed in natural philosophy.'
"Armed with this authority, chemists, electricians, astronomers, and mathematicians may surely claim to be admitted along with mere descriptive investigators of nature to the honourable and convenient title of Naturalist, and refuse to accept so un-English, unpleasing, and meaningless a variation from old usage as physicist."
Sir W. Thomson, Mathematical and physical papers, London, 1890, vol. ii., p. 318
An interesting analysis of the objections to Scientist follows in Sydney Ross' paper:
"The argument that followed about scientist came too late to affect the shift in usage by which all knowledge save that of the material world had been excluded from science; that change had been accomplished a generation or two earlier, had been almost universally accepted and was no longer open to debate. But by establishing scientist as a specific designation, the new position of science would be buttressed and immeasurably strengthened. Was there no champion to repudiate this exclusive title held by a small group of professional men, the knowledge of other men being deemed no better than nescience or ignorance? There were, significantly enough, no opponents to scientist who objected to it on that score. They seized on the irregularity of its construction: 'scients or savants but, please, not scientists.' They also played, for all it was worth, their conviction (alas! a false one) that it had a trans-Atlantic origin. Those who objected to scientist wished to uphold the worth and dignity of the study of science. By inescapable mental association, attributes of the word and of the thing are equated. The ignobility of scientist, as long as it was felt to be so, lessened the stature of those designated by it. After many years the current ran the opposite way, and the name acquired the honour paid to the individuals who carried it. At first, however, and until ca. 1910, careful writers in Britain used scientist only as a colloquialism, the phrase 'man of science' being used in formal discourse or writing: for example, the title-pages of the earliest volumes, from 1888 to 1914, of the great Oxford English Dictionary carry the line: 'With the assistance of many scholars and men of science.'"
Ironically, one of the most notorious opponents of scientist was Thomas Henry Huxley, an English biologist, known as "Darwin's Bulldog" for his advocacy of Charles Darwin's theory of evolution. In particular, he wrote the following letter to J.T. Carrington, editor of Science-Gossip:
The Right Hon. Thos. H. Huxley, F.R.S.
Hodeslea, Staveley Road, Eastbourne;
December 10th, 1894.
To any one who respects the English language, I think 'Scientist' must be about as pleasing a word as 'Electrocution.' I sincerely trust you will not allow the pages of Science-Gossip to be defiled by it.
I am, yours sincerely,
Thos. H. Huxley.
By mentioning electrocution, an American ' blend ' of electricity+execution, Huxley showed that he (wrongly) considered scientist to be an equally unscholarly Americanism. As Sydney Ross notes in his paper, "what may be regarded as the last comment on the controversy was made unconsciously by a modern biographer of Huxley: on the title-page of his book, in all innocence, he applied the hated word to the great man himself. This was indeed a cruel stroke by Fate, yet so delightfully apt that no Mikado in search of poetic justice could have improved upon it."
Interestingly enough in this context, the author of the term scientist, William Whewell, was also a violent anti-evolutionist and, unsurprisingly, in later life neither he nor Darwin was over-keen to emphasize their earlier intimacy, acknowledged in Darwin's autobiography by the statement that "next to Sir J. Mackintosh he [William Whewell] was the best converser on grave subjects to whom I ever listened".
The last section of Sydney Ross' paper is devoted to the scientist modern (back in 1962) 'usage and abusage':
"In the excessive popularity of science, scientist, and scientific in the newspaper vocabulary, the process of extension is carried nearly all the way to nonsense. These words, according to a modern scholar, are 'used too much, and by the wrong people'; they are 'vogue-words' of high prestige, bandied about for effect, but based on vague and imprecise notions of what they stand for. The patient, dedicated men and women, the living realities of the word scientist, working in laboratories and communicating in an esoteric language only with their peers, do not satisfy the general craving for definitive answers to social, economic, and political problems, which, so the great half-educated has been led to expect, 'science' has it in its power to deliver. An abstraction named 'the scientist' has been given form in people's minds as a new figure of authority, corresponding to the priest or witch-doctor of a more primitive culture, whose 'scientific' statements can be accepted with child-like reliance. The notion is dangerous not merely because it is untrue but because it is irrational. The quest for absolute scientific validity is as hopeless as the quest for the philosopher's stone. There may be incidental good in a political or religious philosophy that claims 'Scientific' authority and that stands ready to identify itself with the ready-made image in the popular mind of the infallibility of science; but the willingness to assume and exploit that role betrays the unprincipled shrewdness of the publicist."