A minority of people drive drunk and alcohol is not illegal. We don't respond to that minority by illegalizing the substance, we simply punish the people who are responsible for the wreckless behaviour.
Similarly, the majority of people who smoke pot are not going to endanger the public, mostly by the very virtue of the drug itself. Pot smokers are some of the most innocuous people I've ever met.
I don't think many people grew tobacco for their personal use before it became a controlled substance. Pot is different in that a large number of people grow it even while it's illegal. If they try to control it by outlawing grows, it won't work. The grow ops will continue.
Still, the government and industry could make a profit off of it. Look at CA. Even with all of the undeclared grow ops happening and the FDA continuing their raids, it is still netting the state hundreds of millions per annum. This is a cash cow just waiting to be milked.
If you look at the historical reasons for why pot was outlawed, the reasons are just as stupid as the ones you hear from the anti-gun crowd. It's a bunch of hysteria that doesn't add up in the end... but as history shows, it's not about making sense, it's about which group can shout the loudest that gets the laws passed.