Aside from the numerous medical uses for marijuana (especially in regard to cancer), we have to weigh its every day risks and costs to the non-medical consumer. Doing so gives us a pretty clear picture: prohibition of marijuana makes even less sense than the earlier prohibition of alcohol… and even that didn’t (and in some nations still doesn’t) work very well or help anyone.
Discussions about drug consumption should be exactly that, and not about legal threats. Substance abuse can be a real problem, even with substances that are not physically addictive, and they should be dealt with as social problems instead of criminal ones.
The graphic below is basically right, and marijuana seems to not just grow brain cells because it also improves connectivity, and even though alcohol also doesn’t kill brain cells in non-extreme doses (or when not used as a primary source of carbohydrates), it is easy to understand why an increasing number of nations and states are moving to legalize and medicalize cannabis.