Sorry I haven't read the whole thread
Of course it's possible for non Christians to love others in a real, sincere way; I know such people. But often I find that people who have been deeply hurt in the past are almost afraid to forgive, love, and trust others. This is where God can really help. As Lewis said once, it's not that Christians are always better people. It's that they are changed people, and better than they would have been otherwise. Angry and bitter people get better, and those who are already kind and loving improve even more. I know that I found it really difficult to forgive people, let alone love my enemies, before I became a Christian. I'm not trying to say that I'm superior to non believers, because it is only by God's grace that I have been changed, and I am still far from perfect and have a long way to go. Christians are just as guilty as everyone else.
I think that as we get to know and love God, we are transformed. In fact you can't truly know Him and not be changed somehow. As we experience His love, we are supposed to start loving others in a similar way...it's a deeper, more meaningful type of love than the world offers. It is self sacrificing, not selfish, and goes beyond tolerance. I think CS Lewis said something very profound in 'Weight of Glory':
"And our charity must be a real and costly love, with deep feeling for the sins in spite of which we love the sinner - no mere tolerance, or indulgence which parodies love as flippancy parodies merriment"
This is how God's love is, I think. He wants to take away our sins, but He loves us as we are and we don't have to make ourselves holy to approach Him. After all, Christ died for sinners, not for perfect people.
I guess what I'm trying to say is that some of what is often called 'love' in our society is very limited and shallow compared to God's love, which we are told to imitate as Christians. This is not because we belong to a particular religion (this has nothing to do with religion!), but because we really do need supernatural help to truly love
everyone, especially enemies or people we see as 'unworthy'. It's still a struggle for me, and I guess it would continue to be so while I'm on earth.