Social justice activists like myself have a tendency to construct a lot of rules about which words to use or avoid. For example, “gay” is preferred to “homosexual” because the latter is too formal, clinical, and distant. On the other hand, “homosexual” may be acceptable when it’s used in parallel with “heterosexual”, or if it’s contrasted with “homoromantic”. These rules can be frustrating to learn, but they have some rationale behind them.
And then there are other rules which just don’t have any clear rationale. For instance, “gay” is to be used only as an adjective, never as a noun, and certainly never as a plural noun (i.e. “the gays”). Why? We don’t have a problem with using plural nouns for other identities, such as “Americans”, “liberals” or “atheists”. Even other sexual orientations are usually acceptable, as in the case of “lesbians”, “bisexuals”, or “asexuals”.
On an individual level, the only rationale is that “the gays” just sounds wrong, and conjures negative associations. It makes me think of conservative preachers talking about all the evil things the gays are up to.
On a broader scale, this is a clear example of signaling. Following arbitrary language rules indicates that a person has taken the time to educate themselves and exercise a little empathy.