Wife and Mother in Law believe in spanking while I'm 100% against it, how do I deal with this?

So this pisses me off. My MIL and wife believe spanking is an appropriate discipline. I firmly disbelieve in physical discipline. I believe a parent can effectively communicate what is right and wrong without physical discipline all it takes is a lot of patience and repetition. I feel like use of tone can be a little too harsh already.

Anyways, how do I get them on the same page as me?