Confused

I do not understand why there is so much support for legalizing "pot".   We have spent billions to discourage the use of that other noxious weed, tobacco, and placed warning labels on cigarette packages telling of the health hazards of its use. Am I to believe there are no health hazards connected to smoking weed. There are health hazards involved in breathing exhaust fumes, wood smoke,  heck,any particulates . Pot is exempt from this danger? I acknowledge there is no scientific evidence of pot causing respitory disease , or cancer. There are few studies done. There have been studies  done that indicate brain changes and cognitive decline in marijuana users but this evidence has been ignored by legislators in Colorado and the public enthusiasm for legalization of use. I have no moral quarrels with  those who use weed or tobacco but it does seem that to promote use of one while decrying the use of the other is hard to justify.