Well, I guess you are having trouble distinguishing between proper terminology and slang. It's okay to call a person by a slang name if they're good with it, it's also okay to use a proper name regardless of whether they're good with it or not. Considering that the word "gay" is - or actually was slang and is now a more preferred term than "homosexual" makes as much sense as women saying "we hate the word breasts", so we'll start using "jugs" or "hooters" too describe those things on our chest or insisting we stop saying "vagina" and instead use "vajayjay".
gay
adjective, gayer, gayest.
1.of, relating to, or exhibiting sexual desire or behavior directed towarda person or persons of one's own sex; homosexual:
a gay couple.
2.of, indicating, or supporting homosexual interests or issues:
a gay organization.
3.Slang: Often Disparaging and Offensive. awkward, stupid, or bad;lame:
This game is boring and really, really gay.
4.Slang. inappropriately forward or bold; overly familiar; reckless:
Hal 9000 got gay at the Christmas party and suddenly swept his boss's wife onto the dance floor.
5.Older Use. having or showing a merry, lively mood:
gay spirits; gay music.
6. Older Use. bright or showy:
gay colors; gay ornaments.
7.Older Use. given to or abounding in social or other pleasures:
a gay social season; the Gay Nineties.
Now, you see that the gay community has hijacked the word gay, and even taken over the number one spot in meaning. The original use of the word is not found until #5. In fact, if one uses gay in it's proper meaning, the gay community rises up and claims homophobia. No longer can we use "gay" in normal conversation, and hearing the Flinstones are having a "gay ol' time" is a little awkward. According to your article, homosexuals were using the word "gay" as an almost covert word that people outside the community wouldn't know. Logically speaking, when homosexuality became more mainstream, the gay community should've abandoned the word and stood proud with "homosexual". It's almost like "First Nations" rejecting that name and insisting on "Indian".
Now, If I say "This picture is gay", I'd be right and proper (see #5 and #6). It would have nothing to do with the homosexual community, yet I would be branded a homophobe (#3) for doing so.
And, what about the word "queer"? Shouldn't that be offensive? If I call someone "queer" shouldn't that be offensive?
Queer
kwir/
adjective
strange; odd.
"she had a queer feeling that they were being watched"
synonyms:
odd, strange, unusual, funny, peculiar, curious, bizarre, weird, uncanny, freakish, eerie, unnatural.
antonyms:
normal
2.informal offensive
(of a person) homosexual.
denoting or relating to a sexual or gender identity that does not correspond to established ideas of sexuality and gender, especially heterosexual norms.
"queer geek culture has featured gay themes since the 1980s"