It appears that your friends want to be friends on their terms and your opinions and feelings don't mean anything to them. I would continue to be friendly with them and if they make the decision to terminate the friendship then it is their loss.
From the sounds of it though, it is a lost cause. Unfortunately, they sound like the typical anti-gun person who will not listen. They accept what fits their agenda and reject everything else and no amount of reasoning will work.
You are free to choose, but you are not free from the consequence of your choice.