Put the shoe on the other foot- would you ask/make him to do something he would be morally opposed to? AND would he do it?
If he knows how strongly you feel about this and insists you do it anyway that would be a certain deal breaker for me.
Is it something you can both compromise on? Like if he wants you to do xyz but you agree to only do xy?
Why is it so important to him? Why does it mean more to him than you and the kids?