In theory I think if the DEA could make like the Cobra and crack the fuck down it'd be a good thing, but kids would still be growing pot in their backyards.
The Iron Rule of Prohibition is that the more that's illegal, than the harder and more concentrated drugs will get. So during the Prohibition of alcohol, liquor became much more widespread because it was so easy to transport and got you so much more bang for your ounce than beer.
I don't think America would be a better place of meth and heroine use were rampant, but I have a hard time seeing how weed is more damaging than booze or SSRIs.