It seems pointless to punish evil doers with earthly punishments when they will go to hell anyway for their bad deeds. I understand it's a good prevalent to prevent further crime but it seems strange we are punishing wrong doers when Allah will in the end?
Usually to act as purification or to strongly discourage it or when it affects someone else. I mean the punishment for murder is death as it will discourage people to kill and cutting of hands for stealing as it will discourage people to steal. Sins like murder and stealing not only affect you but also others and thus, punishment in this world.
The Prophet Muhammad (S. A. '. S) is noted to have said, A wrong done in this world that is punished, will not be punished in the hereafter. A wrong done in this world that is not punished in this world will have a severe punishment with Allah.
As we have people that commit crimes against people and or society as a whole, we are duty bound to assist them. Being Muslim we must be at the forefront of building a safer world for our children to live in. So, when we have the opportunity to correct a wrong we are actually helping the wrong doer closer to Allah's forgiveness. Allah says in Al Qur'an, "oh ye that believe enjoin right and forbid the wrong." That is an order not a request. We are duty bound by this. There is a saying, Am I my Brothers keeper? The answer to that question is yes. We help our brothers in right and in wrong. You might ask,I understand in the right however, how do we help in the wrong? You do that by deterring your brother from doing the wrong. That gives you and him/her a blessing. As Salaamu Alaykum wa Rahmat Ullahi wa Baarakatuh.