I'll admit, I haven't read this whole thread, but I want to say my piece.
I write yaoi and slash, yet I didn't find this offensive in the least. There is a lot of bad yaoi out there, but I do my best to keep things in character while being as realistic as possible. I don't get much constructive feedback, even though I would love it. I think I do a decent job, but my audience is heterosexual woman, and I myself am one as well. No, I don't know what gay sex feels like in the least, but I do my best, and this is mostly based on what I read in other fics that I enjoy.
So what was my point? I have no idea. I think my writing is decent, better than most of the yaoi "crap" that is out there, but I am no where near as good as I want to be. I want my fics to be as realistic as possible, even though they are based in a very unreal fantasy world.