I don't see what the problem with legalization would be. I think one of the main reasons it isn't legalized is precisely because it would be so difficult to tax. Unlike tobacco, pretty much anybody can grow it pretty much anywhere very easily, and certainly nobody can tax you for growing some plants in your backyard. Plus, most pot smokers are pretty wary about what the cigarette companies would do to it, and I think most of them would prefer to grow it themselves or get it off a friend who does. Just imagine how much easier and larger homegrown crops could be if it were legal.