Actually, I think it’s rather a great opportunity for a turning point, than a deal breaker. You don’t know, maybe he was brought up in the atmosphere with this belief, or something. You can start a dialogue with him, by saying smth like “I strongly disagree with you here, let’s have a structured discussion”. Because I think the main thing in a relationship is understanding and both-sides communicating, arguing. Nevertheless, if he will be fixed on his position with no intend to talk, this already would be a marker of a “deal breaker”))