Why isn't weed legal?

My thought is that if weed was legal, the government could oversee it, try to make sure people aren't abusing it (maybe set limits on how much one person could buy), tax the hell out of it, make sure it's not being sold to minors, etc. Obviously there are still ways around all of this (consider all the problems with underage drinking) but I think it would be a start.

They don't know as much about it as they need to, before they could legalise it. The physical health effects are just as bad as smoking, but the psychological effexcts are much worse for cerain people, i think in a report they said about a quatre of the population of england would experience psychological effects, if everybody smokes. these are things such anxiety, depression, paranoia, etc. in some ways it would be better if it was legalised. they could give guidlines on how much people should take, the government could tax it, and at least if you are buying it from a company you'll know that nothing else has been added to it. for example, people tend to add plastic and other materials to solid hash, to spread it further, make it heavier etc. but i think governments tend to not want to encourage it's use.

Conspiracy 1: Cannabis is illegal because though it has to compounds to cure most illnesses, the FDA banned it to ensure a market share for the pharmaceuticals. If everyone smoked weed for their pain/depression there would be no need for xanax and such.. Conspiracy 2: Governments all over the world ban the use of cannabis because it promotes laziness in it's people. A country full of lazy stoned people? For me, it can only be good; but from their views..no output = no earnings = low gdp = back to third world status. The above are all figments of my active imagination.