Yep. Big business doesn't want it legalized either. The booze companies (and the tax man too) would lose out since you can grow killer weed in your backyard.
I think you are right in stating their fear, but I think in the long run that fear is misplaced.
First, I dont think that most people have either the time or ambition to grow their own. You could grow tobacco in your basement but there is no reason to, nor is there a reason to brew your own beer.
Pot is not much different than other low level drugs and the tax revenues that could be generated through legalization would only be dwarfed by the staggering cost savings in terms of enforcement, prosecutions, incarceration, probation and parole management.
I have no doubt that there would be significant negative societal consequences to such a move; however denying the billions in profit to the criminal organizations behind this increasing violent industry is tempting.
A younger business associate of mine is harvesting a small crop. I gave up the desire toking about 25 years ago.