Well this is a hard one but born again Christians do believe that only the saved will go to Heaven and that only those of us who go before God and ask for forgiveness and guidance in our lives will go to heaven hence saved and once you've given your live to God then your born again.
To say that all those not saved our ultimate sinners is incorrect as we are all sinners but Christians are only different because Jesus gave his life so that we could be saved from hell.
Yes none Christians will not go to Heaven is the belief and the aim is to tell everyone of God's story but the choice is for each person. Doing good things and living as a saint doesn't cut it as God word says that we must believe in him with faith and hence no evidence will ever be found as this is totally against the bibles teachings you have to love and believe in him without seeing or finding evidence.
You have your believes and they have theirs and these no point not being friends because of it you need to just respect each others feelings and your Christian friends will believe in God that he will deal with any issues required.
As for criminals etc it all boils down to the same points that a sin is a sin whether it's a little white lie to save someone's feelings, sex outside of marriage or murder they are all sins and yes Christians believe that all sinners will go to hell, but ask for forgiven and admit that they are living to God's well will lead you to heaven and Gods side.
As for the heated discussion your friends lives are guided by God everything they do is done with God and they are God speakers on earth so try to ensure they live to this as Christians.
God's word is that he loved everyone and hence Christians aim to love everyone no matter what they do, have done or are going to do and so they are friends with none Christians, this is not an aim to convert everyone as this is not a Christians job it's their job to tell God's word and let God move in each persons to bring them to a place where they decide to give their life to him and get saved.
They are your friends so avoid conversations regarding belief as they will always end up heated as yes they are following Gods word and as a none believer they will find it hard to not understand why you can't believe like them, but they like you for who you are so you should both just accept where your at and leave the beliefs at the door - they will be unsure about your discussion as they will not want to loss your friendship.