We generally think that the purpose of words is to communicate ideas; thus words should be relatively stable to maximize comprehension across the broadest number of people. Of course, many people prefer to use words as fad items for purposes of status marking so that they can sneer at those who aren't up to date. Eventually, this facilitates demonizing and punishing those who aren't with it.
From the New York Times:
To most ears, it probably sounds inoffensive. A little outdated and clinical, perhaps, but innocuous enough: homosexual.
But that five-syllable word has never been more loaded, more deliberately used and, to the ears of many gays and lesbians, more pejorative.
“ ‘Homosexual’ has the ring of ‘colored’ now, in the way your grandmother might have used that term, except that it hasn’t been recuperated in the same way,” said George Chauncey, a Yale professor of history and an author who studies gay and lesbian culture.
Consider the following phrases: homosexual community, homosexual activist, homosexual marriage. Substitute the word “gay” in any of those cases, and the terms suddenly become far less loaded, so that the ring of disapproval and judgment evaporates.
Some gay rights advocates have declared the term off limits. The Gay and Lesbian Alliance Against Defamation, or Glaad, has put “homosexual” on its list of offensive terms and in 2006 persuaded The Associated Press, whose stylebook is the widely used by many news organizations, to restrict use of the word.
The Decline and Fall of the ‘H’ Word
For Manys Gays and Lesbians, the Term ‘Homosexual’ is Flinch-Worthy
By Jeremy W. Peters March 21, 2014
One not completely obvious bug with jettisoning "homosexual" for "gay" is that "homosexual" fairly covers both "gay" and "lesbian." In other words, "homosexual" is non-sexist while "gay" is clearly male-dominated. As a lesbian leader pointed out once, "We're not gay, we're angry!"
But the sexism of gay is not really a bug, it's a feature. After a number of years of persecuting older individuals for saying "homosexual" instead of "gay," then the persecutions can begin of people for saying "gay" instead of "lesbian and gay." And then the bisexuals and trans will have their turn persecuting the losers who say "lesbian and gay." And then the different flavors of trans will get to persecute those who aren't paying adequate attention to their immensely important differences, and so forth ad infinitum.