Disclaimer: I don't necessarily disagree with any critiques raised about the problems (the treatment of) with female character in slash, but I would argue that happens in het as well, or with drawing attention to the erasure of female characters in slash.
I hate it because I never see anyone ask 'why het?' (or 'why femmeslash'), as if they were entirely different genres, with no possible overlap, and that one (because I kind of think femmeslash is so small it doesn't get too much attention) is 'natural' to write and the other needs some kind of explanation.
Just for the record, I ship1
het, femmeslash and slash, although not equally, and a lot of it just doesn't get written down. (In one of my completely unwritten original universes, though, where I cunningly flipped my human counterpart2
's sexuality (90% mostly bi; 10% mostly straight/gay)--there
are about equal numbers of same/opposite sex relationships, for reasons I'll bore you with later
when I've thought them out better
I don't see why anyone of those should need any more explanation or justification than others, because I ship: a) because the people/characters have great chemistry; b) because they're pretty together; c) for the lulz, regardless of whether the pairing is f/f, f/m or m/m.
Of course, I also tend to write ficlets, where it'd make sense to have just the characters shipped in the story; a certain crack!fic which is currently eating my brain
stars an ensemble cast and will be
true to its source
Conclusionish: Cass dislikes "why slash?" questions, ships (femme)slash/het, ships for a variety of reasons and doesn't think slash and het are so different one needs explanations and the other doesn't. 1 Also, I think up noticeably less het because a) sports rpf lends itself more to slash and b) I find (femme)slash more aesthetically pleasing.
2 They're not Earth humans, but they're still what we'd instantly recognize as humans. The biggest difference is tolerance to magical radiation: 'my' humans would die without it, we'd die from exposure to it. Another is sexuality, as well as some more things influenced by different physical circumstances (different type of sun, larger planet with several moons, different kind of solar system, magic, etc).