>And BTW by "jail time" I mean serious jail time, as in multiple decades of jail time, and/or life sentences if necessary.

Have severe jail sentences rid the world of illicit drugs users, murderers, cutpurses, burglars, vandals, fraudsters, rapists or anything else?

If the chance of being caught and going to jail is lower than the expected gains of not getting caught, criminals gonna criminal. How do you aim to stop that with a threat? Throwing someone in jail is "too little, too late".