If you get more than before, the punishment might make some sense in a deterministic world so reinstate it.
It's just as likely you go back and perform whatever magic you need to to delete punishment for murder, then zip back to 'now' and see the world is a global panopticon making sure people don't murder each other.
Some of this may be a failure of people to realize what P !=NP is about, especially in non-linear systems.
Small perturbations in an early state of the system can lead to wildly different outcomes in the final measured state of the system. You can't determine what that will be in non-polynomial time. The only thing you can do is make probabilistic models by running a full simulation in real time (or reality with a time machine I guess).
In weather you have things that are chaotic, but follow rules and don't create them. Things can surprise you, but you'll mostly center around particular solutions.
With humans this gets a lot more complicated because you are messing with systems that follow fixed rulesets (chemistry) and things that follow self modifying rulesets (social conventions). A very unstable system on top of a semi-chaotic probability state.
A good example of this would be if I deleted the concept of rain from the human mind and all of human history and knowledge. Humanity would be very surprised on the thunderstorms that popped up, but they'd continue on just as they did before.
Now lets imagine I delete the concept of all gods. Would the idea of gods come back, for sure. Would they look like our gods now. Very questionable indeed. We wouldn't be getting jesus back. And the new set of religions could have wildly large effects on how the people act.