Hmm... that's possible. Although we've seen marijuana legalized in some states already, maybe others would follow eventually? I don't know if weed will cause brain damage in the long run but it seems that it don't cause people to commit crime on the scale that meth does. If it can be used as a "soft" drug to prevent people from using the "hard" ones, than I'm in favor of its legalization.
There is no scientific proof for the argument that the usage of marijuana results in brain damage. Humans have been using marijuana for many thousands of years, and according to the experts the positive benefits of marijuana outweigh the negatives by a wide margin.