While I can't find any "proof" for the existence of an after life in your argument, I will say you make a fairly good argument for why we should want people to believe in an afterlife and a just God.

The only argument one can make to a sociopath to convince them not to be soiopathic, is an enlightened self interest argument:

If you commit criminal acts and get caught, society will punish you.

Truly sociopaths personalities are notoriously indifferent to the above argument.

They know that society isn't really all that good at meting out justice or finding and punishing criminals, either.