[zaarn]

If we discovered free will doesn't exist, provably, which is my current position, I don't think anything would change.

The illusion that we have free will was strong enough that we used law to keep everything in line, make people responsible for their actions, etc.

I see no reason why either side of the coin would or should stop that behaviour.

If our actions are a result of our environment, shouldn't the environment to the best of our ability be changed such that negative actions have a lower probability of occuring?

With free will you punish people for a crime because it's their fault. Without you punish people to create an environment in which crime is not desirable. (Though resocialization / rehabilitation is probably a better option)