IMO, I honestly prefer to steer away from real person slash fan fiction mostly because the people are REAL and not cartoons who we'll never know in real life.
I've never really read any of these slashes myself but it's a bit awkward for me because even if the people who are writing the slashes are talking about the characters, I have a hard time separating real life characters from their actors. So it's like I'm hearing about the actors doing #$%& and that's what's weird.
For anime characters, it's not like they're people in real life so it's less awkward to read about them in slashes.
So to sum it all up:
anime yaoi = non fictional characters AND people and the person doesn't feel guilty reading about them doing anything because they're not real.
real life yaoi = awkward and weird because the non fictional character is portrayed by a REAL person and so even if you're reading about their character, you'd still be imagining the actor doing some unimaginable things with some other actor and you'd feel a sense of guilt and sort of like some sick pervert who fantasizes about random people doing it with each other.
And if I don't like it, I just don't read it. I actually haven't read any before but I've heard of these things. But if I WERE to read one, I think I'd feel a bit embarrassed while watching a series (never seeing the character the same again), depending on how intense the slash fan fiction was.