I have seen people mess there lives up from pot. My sister and her husband for example. My sister's lungs collapsed and she didn't smoke cigarettes so I believe that pot smoking can affect the body in harmful ways. Both my nieces born of my sister had birth defects and birth defects do not run in our family. She smoked full time during both her pregnancies. I believe it was a major factor in those birth defects. I also saw how careless they became over the years in their use and there attitudes. It eventually ended up helping ruin their marriage because one (my sister) wanted to get clean and sober and he didn't. He chose to continue and that ended up one of the factors that ended the marriage.
I know that it can be said about almost anything taken in excess, maybe it should be treated like alcohol. Legal to use but don't drive under the influence or have it exposed publicly or laws similar to alcohol. I have seen people mess up their lives with alcohol, with pot, with prescription drugs, with adultery, with video game addiction, so I understand both sides of the argument.
I will say that people who claim that pot is not harmful or that it is okay as long as you are at home miss some of the points. Do it at home...hopefully you are a single adult and not doing it while you are pregnant, or in front of your children or stoned while your high school kids come home from school...then you are affecting people even in your own home. I believe it is harmful, can be addictive and can be abused and people who use it should have a huge responsibility of the consequences they bring home, especially if you are raising children. Just because you do it at home, doesn't mean no one else will be harmed.
Again, I am not against the use of pot and maybe it should be regulated like alcohol but please don't blow smoke up my ass and say that it isn't harmful physically, mentally, etc. because it is and can be just like any other drug out there. I have seen the effects first hand and nobody can tell me different. By the way, I am 39 and have probably been on this earth more than most here and have seen and experienced more than most, take my word for what it is worth.