Mr LaBute, in the same kind of language you use in your play, please give me a 'f.....g' break.
LaBute is always being accused of misogyny, as if he himself is speaking through his very negatively characterized male characters. I take his work to be an attack on misogygy. And this play is another example of that.
You take Bobby at face value when you speak of his high moral values. That's his justification for himself. But behind his words we very clearly see what he really is. He defends himself against the charge of wife-beating yet the first time he and his sister argue he nearly punches her in the face. THAT'S who he is, never mind what he says. I don't wnat to give the plot away here so I can't really speak of his true feelings and attitudes to his sister but clearly he has a far different agenda than the one he proclaims.
This is typical of LaBute characters and it's one reason his plays work and actors like to take them on.