Yaoi is written for straight women by straight women and represents little of what actual gay relationships are like. In the end, they tend to objectify and oversimplify gay relationships to a degree.

Yes, it's a fantasy. I get that, but it's not emphasized enough that it doesn't represent any healthy relationships.

EDIT: They aren't portrayed as rapist and victim, though. These relationships are often portrayed as a pair of star-crossed lovers and an ideal romance to aspire to.