This is a very loaded question. I do not think that dating a non-Christian is in any way a bad thing and have nothing against this personally. That being said there are many different circumstances that someone could fall into outside the Christian religion. We could be speaking of someone Buddist or we could be speaking of someone that is Atheist. I do not want to say that any religion is bad or good outside the Christian rhelm and do not wish to start an argument over what everyone believes but both of these situations would bring different feeling towards the thought each. How passionate the other person is with their religion is possibly a large part of that also. Would their only purpose for being around you be to attempt and convert you? This would be a situation that may cause a conflict between your beliefs and your feelings. That would be bad and that I would not approve of.