When the plague swept through Europe it killed like every third person. That some people are immuned is no reason to expose those who aren't.
Yes, some people can handle marijuana and it does not screw up their lives. A *LOT* of other people cannot handle it and it does.
Should we just throw those people away? Should our laws only reflect what the strong can survive?
Shall we outlaw all alcohol and tobacco products because some people can not handle it???