Should be legal, but regulated. Just like alcohol, weed shouldn't be available to minors. Using should be an adult decision made by adults.
Yeah, I know. Minors get booze, and they'd get the weed too, but it would be harder than it is now where no I.D. is required.
Legalization would disrupt an entire criminal enterprise of distributors, and stop a lot of people from going to prison for possession who should never be there anyway.
I don't think that the fact that people could grow their own is a determining factor in pot being illegal. True, some would but most would be happy to buy tailor mades at the store and pay the associated taxes.
Just like some people like to brew their own beer, or make their own wine. But most prefer to just buy it.
The real reasons may get too political (if this isn't already) but suffice it to say that it has to do with control and personal moral decisions being forced on a populace.
P.S. I don't smoke pot either.
(Ignore Phineas, Freewheelin' Franklin, and Fat Freddie there

)