I feel only a little guilty for badly injuring them
Guilty? What did they do?
Yes, I fired back at them and then they were going to attack me after that. They deserved it.
You are behaving in  an irresponsible way by not feeling guilty for injuring someone. You should feel more empathy towards the pain of others.
It's not like I killed them or anything I would be in jail for it.
Shooting someone sounds like attempted murder to me. You could have hurt someone seriously or killed an innocent bystander. It is quite telling about your self to not feel guilt or remorse.