While I agree with the rest of your post, pot does NOT "kill brain cells"... It does certainly have some very negative effects, social effects being one of them. Brain cells it does not kill however.
Ya I remember seeing/reading something that showed how the tests that "proved" it killed braincells were done: They strapped tubes to monkeys faces and just pumped and pumped smoke until they saw the results they were looking for.
Of course that amount of constant smoke and no air is going to have negative effects