how about if someone wants to go out an snort lines until they get addicted, can't keep a job and then starts stealing from their friends and family (not to mention the burden on our health care system)? Sure, I understand the whole "it's your body, do what you want with it" line of reasoning (although I don't agree with it), but in many cases, drug use affects many, many people other than the user. Drawing the line at "things you can ingest" doesn't seem rational.
In this case, however, I think pot is reasonably benign. go legal. re: regulation, the above poster who said something about not underestimating the laziness of your average person (pothead) had it right.