To be fair, that was advice for nonviolent resistance against the state, in a context where slapping someone's other cheek presented social difficulties to the oppressor. In order to slap someone's other cheek you had to use your unclean left hand, disgracing yourself by vulgar behaviour, or use a forehand slap with your right hand, which implicitly acknowledges the victim as your social equal. Turning the other cheek is a great way to fuck with the Romans.

The New Testament is full of practical advice for anarchist Jews to use against the state.