In Book Three, Chapter One of Mere Christianity, Lewis proposes that there are three parts to morality. The first part is universal: don't do things that hurt other people. The second has to do with one's own inner moral condition, and the third with one's relationship with God.
It's so much easier to live in the first part of morality. Who wants to hurt people? I doubt there is anyone who wakes up in the morning and says to himself (or herself) "Oh wow! Look at how the sun shines so bright and the weather is just right! Perfect for carrying out my diabolical plan to hurt as many people as I can today! MWAHAHAHA!"
But we manage to hurt people any way. I imagine that most of the time, it is because of selfishness and a lesser developed inner moral condition. But sometimes we hurt people because we can't agree with their choices. We can't agree to "live and let live" (though I do think we can agree to "live in love") because the choices being discussed are so clearly against what God has said in His Word that we can not in good conscience condone it. I suppose on some level we risk causing them more hurt my condoning things that must not be condoned, but the person involved may not ever see it that way.
I guess the point of my little tangent, which lost Lewis somewhere along the line, is that morality is tough on any level. I am so thankful for forgiveness.
Please visit my friend Sarah Salter if you'd like to read a more in depth discussion of this Chapter of Mere Christianity.