That's why some games give you the option.
Remember this part in The Goonies II game?
That's right. They put a defenseless eskimo or a barely mobile old man in front of you. And they give you the option to hit them. And I'm sure you will. Why? Because you're evil.
But my personal, all-time favorite "tough decision" was in Tokimeki Check-In!:
Damn these Japanese hentai games and their morally-complex decisions! Why don't they give the player some other options, like "drug Ayumi" or "wait until Ayumi is asleep"? Seriously, though. I wonder how many people chose the second option. If you choose the first, Ayumi won't marry you (what's that? You don't want to marry the guy that raped you? I can't imagine why.)
Can you think of any games that actually allow you to attack your friends?