Well Jesus never said that. He didn't say "Resist not evil, unless it's really really evil like Hitler", and he didn't say "whosoever shall smite thee on thy right cheek, turn to him the other also, unless you don't feel like being a pussy today".

I find it rather amusing how often Christians rationalize acting contrary to Jesus' teachings. If I believed there was a text of moral precepts that were thought up by the omniscient creator of the universe, I would take them very seriously! But then again, the Bible is a very difficult text to take seriously...if I tried to follow it I would have no eyes because I lust after girls a lot and Jesus says eye-gouging is the correct solution to that.