The next few years will demonstrate legal recreational use won't cause the Reefer Madness Armageddon. More people will recognize the stupidity of squandering billions on the prohibition/prison industry and a tipping point will be reached.
What I think is more likely is that they will find legalizing a dangerous drug to be a disaster for their society and economy. I predict the number of addicts will approximately double, car accidents caused by being under THC influence will increase, addictive behavior will cause more families to suffer and to be torn apart, bankruptcies due to marijuana consumption will go up, and their economy will erode as until they finally realize what a horrible mistake they made.
Marijuana is a dangerous schedule 1 drug. It should stay that way.