I'm not convinced that because Christians believe that God loves them, that this makes them love - oh yes I think it helps to have been loved by others, but ISTM that Love is something humans do innately.  I'm therefore also not really convinced that Christians Love more than Non-Christians - if they do, then it's possible that people who want to Love are naturally drawn towards institutions and mindsets that promote Love.

I suppose we could say that Love causes Love to grow, and if we believe that God is Love then saying that Love causes Love to grow is the same as saying that God causes Love to grow.   The problem is that many Christians see God as an external character, a personality who does 'his' loving from the outside, and that adds in all sorts of complications that clearly don't hold true.  If we simply stick with a God who actually IS Love, then whether an atheist Loves or a Christian Loves, it makes no difference because both Loves are God.