Perhaps they don't realize God only endowed us with two cheeks. Personally, my patience has ended.
To have one's face slapped in Jesus' day meant then what it means today: it's an insult. "Turning the other cheek" means that we should tolerate insults, to some degree anyway. It has nothing to do with pacifism.
After all, Jesus told soldiers to be fair and not to be extortionists. He didn't tell them to lay down their arms.