"Why does popular gay ship bash on popular straight ship?" sounds like a very, how to put this, fandom newbie question to me. (Tho to be fair most people on tumblr look like newbies to me.) Slashers have hated on het for yonks. In particular, if the het ship is canon, there will be massive amounts of bashing on both the het ship and the woman in that ship. Traditionally, I recall this being blamed on heteronormativity and misogyny, which have always been painful for a lot of slashers to deal with. But given that the phenomenon is so traditionally common, I really don't feel like we have to reach for racism as an explanation.

I definitely do think kink should be part of the sexuality discussion, perhaps even to the point of considering it a component of sexual orientation (like orientation, it seems to show up early, be consistent throughout one's life, sometimes even overpowers other aspects of sexual orientation, etc). I additionally think of kink as a part of the "queer" umbrella--iirc it used to be, or was close to being there. It certainly was part of the sex positivity movement we got out of the AIDS crisis, though that movement's not been doing as hot as it once was, on tumblr especially.