Yes, I'm an American...and, yes, I realize there are gender-neutral changing areas ubiquitous in Europe and throughout other parts of the world.

I think it's ridiculous when men (or boys) hide their bodies while changing in our locker rooms. But I'm not going to personally attack them for it. I just think it speaks to the flaws of American culture...how, as you've pointed out, American society has stigmatized nudity in overly-puritanical ways.

No, I don't think you sexualize everyone whom you encounter just because you are bisexual. If people are comfortable going nude or partially-nude in public spaces, I'm fine with that -- I don't make a fuss over it or demand that they put their clothes on. But I still have a right to maintain a relatively stress-free experience when changing clothes or showering, and I can't be free from that anxiety if cisgender women/girls see my body fully exposed in that manner.