Speaking from personal experience I have known crack heads, alcoholics and marijuana users. The crack heads and alcoholics will kill you if given the chance. The cannabis users simply get the munchies and chill out. Since the powers that be cannot prevent anyone from using these drugs, it might be reasonable for them to legalize the least lethal.
Parameters for marijuana use can be established when the drug is legalized and age limits are set on its use. We don't need another "prohibition era" , which will criminalize those who will get the drug anyway. It is possible that prohibition of alcohol led to organized crime in America. Prohibition of marijuana may be doing the same thing.
The lesser of two evils does not really make the lesser of the two evils less harmful.
It may become the most harmful.
I'm not so sure that they are the same thing, as for your last two statements.
Give an inch they take a mile.