Have you ever been in a fight? For example back then in the school ground, I wouldn't kick my enemy into the groin. Because that would escalate the rules of the fight into a fight where kicking into the groin is OK. This would have raised the risk of getting kicked in the groin myself.
I can't explain it better than that. I might be wrong, too, when it comes to dealing with the police.
That's like saying that a determined thief can always break in, so why bother locking your doors?