First, and foremost - please do understand genesis of the word. This thread is gay because it's trivial, merry, jolly - it's of jesty tone, no significance and very little importance. Not because we expect it to engage in penetration of male rectum with help of aftermarket lubricant in order to fulfill its sexual urges. That's why we say something is gay, instead of referring to it as "it's sooooooo homophile". Such is the trouble with "borrowed" words and multiple meanings, that it always "offends" those who don't fully grasp the subject.
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How do you support your assertion that the use of 'gay' as a slur stems from a meaning of the word that was obsolete before most of the people using 'gay' as a slur were born and which is irrelevant to the slur anyway?
"That's gay", used as a slur, does not mean "That's trivial, merry, jolly - it's of jesty tone, no significance and very little importance."