It has nothing to do with acceptance and is pretty common place in a lot of gay circles.
Yeah, Gay Until Graduation and similar has been an insult thrown particularly at girls/women for at least a couple decades now in some 'gay circles'. It's kinda like 'Gold Star' where certain groups really love it, but a lot of people find it gross. Some are sensitive to things like that because of the abuse some have had with that.
Part of the problem is as a society we have incredibly limited language around something complicated and important. Yeah, some of them may have been caught up in a trend in their social circle, and but another large part of it, and why some are a bit more sensitive people assuming sexualities are a fad or phase, because of all the shite that's really common in some areas whether with straight people or 'gay circles' (without bisexuals it seems) that bisexuals always 'pick a side' (rather than picking a person) and told repeated 'deep down' we're really straight (usually women) or gay (usually men). That social pressure can get to people. It's fucked with my head at times where I felt I must 'deep down' be one or the other because I had too many lesbian friends tell me that bisexuals just need to get over our compulsory heterosexuality or stop being fakers.
It's seen in this thread where bisexual women who marry men are assumed to have 'actually' been straight - there is a message in LGb circles too that that's the truth, that bisexuals are all just liars and traitors to the cause unless we settle down with someone of the same sex, that we're just playing with people. This ignores a bisexual's dating pool will always have more people of the other sex open to dating us than of the same sex. It's basic probability, even with movements like FemFEB, that more bisexuals will have other sex partners -- and we'll all still be bisexuals.
It would be great to say 'why the hell not try it', but having been someone else's test subject and all the pain that goes with that, I think there is a big difference to someone testing things out on someone and people who seek out and enjoys same sex affection, but has a strong preference for the other sex. A Kinsey 1 for a lack of better word (Kinsey's research had issues, but the scale has uses). I think it would be better if we could have more language around affection and connections though these days it seems more likely to just create another label system than be useful.