For some people, it seems that the degree of objectionability is strongly correlated with the level of aesthetic appeal.thaluikhain said:I dunno, never tried.
A related question, though, do you find the idea of sisters (preferably twins) having sex to be less wrong than other forms of incest? Alot of people seem to for some reason.
Personally, I find incest between brothers equally wrong on the basis of religious convictions, although I'll admit it's not as visually offputting. If you base your objections on genetics, though, then same-sex incest wouldn't be wrong at all.
Still, I don't think it really matters once you reach second-cousin separation.