...except that use by those whose brain is still developing (anyone under their mid 20's) are at a significantly higher risk of causing permanent damage... and there's a significant amount of teens/pre-teens that are getting wasted on a daily basis.Most of the research seems to suggest that it requires an pretty high amount of abuse to effect the short-term memory but nothing conclusive on long-term
But these are extreme cases, requiring someone to get high every single day for years on end. This is far less damaging than the effects of alcoholism.
While I'm certainly for decriminalization, legalization isn't a solution without major caveats in place. For one, there should be stronger penalties for supplying to under 21's (as there should with alcohol).