Yeah...because and because we said so....hardly compelling arguments there...

Perhaps they want your child to attend a Catholic school or something?
Perhaps it's just that you're breaking with 'tradition' and they're uncomfortable with that.
Perhaps they're worried about what other Catholic friends and rellies will think?
(just trying to understand them, still doesn't give them the right to try and dictate your choices)

Stick to your guns, YOU guys will be the parents, just think of it as good practice at making unpopular parenting decisions (I've made quite a few of those unpopular decisions today, NO, Riv may not stand on the piano or eat a tissue :P).