By some guys I mean players and rapists( two random catagories, I know!) .They "play around" with girls; but if their attitude towards their sister is different.

Mostly brothers are protective and some maybe strict when it comes to dating and guys... And then when it comes to other girls their mind frame changes;these same guys wanna "play around" with girls, some are capable of abusing/raping girls. (i k
know players are young and immature; and rapists are more serious and dangerous). But I am interested in the pschyology of these two catagories.
Why this change? I mean the girl they abuse or play around is someone's sister. It seems like I am talking about morals and ethics but I m interest in the pschyology part of it.

Cheers,
Princess :)