The point is not that there won't be a thriving marijuana industry because you can grow your own, but that the industry will not necessarily share the evils of the tobacco industry.

The beer industry is a good example. It's nowhere near as powerful or nefarious as Big Tobacco, and in fact the phrase "Big Beer" doesn't doesn't even exist. Beer companies tend to be fairly benign, while the tobacco industry is famous for stunts like marketing cigarettes to kids and trying to suppress anything that suggests their products are harmful or addictive.

So if the marijuana industry turns out like the beer industry, that will be a pretty good outcome, really.