Some drugs have no other purpose, but to alter the mental state of the user. Other drugs have several very useful purposes. I happen to think the same way about those, although no one thought to restrict their use 'till the AMA dreamed it up at one of their first conventions. My favorite drug, aspirin, comes under assault regularly. There is no constitutional justification for banning drugs, or restricting the use of them to permissions granted by those with a particular license.
There are no individual weapons that are so dangerous to life, or liberty that they need to be banned. The bans in place now are precident setting infringements that are a dangerous threat to Freedom.