I have never known a pothead who was debilitated by his habit who didn't have problems to begin with.
I've heard reliable accounts of successful people being turned upside-down by hard drugs, but not by pot.
I also wouldn't use dangerous stoned drivers as an example of pot's evil, unless you want to declare your belief that alcohol should be banned as well.
I second the vote to go to
http://www.erowid.org to get the full picture. That goes for any drug, for that matter. A wealth of medical information, and personal accounts both sublime and depressing.