language conventions are rarely conscious. they just happen. every now and then there’s a campaign for our against using certain words or phrases; sometimes they stick and sometimes they don’t. but those are conscious i guess. mostly though it just happens organically.
like a perfectly normal word becomes vulgar in time if enough people just say it a certain way. it’s not like people suddenly hold a meeting and decide this word is bad now. it just starts to feel like it after a while, so it eventually becomes so.
yeah it depends i guess. saying “gays and lesbians” in passing is usually fine. but still, while you could say something like “this policy is discriminatory against gays” and not get much protest, the preferred use would still be “gay people”.