Answer: I don't know. There are probably tons of pros and cons to the question. Some of which no one can even know.
Who knows what unforeseeable consequences can happen 10-20 years down the line because of choices we make today? God. Besides Him, no one. For example; the financial "crisis" (which i won't get in to). Who knew the outcome of the choices millions of people made? Who thought to themselves, "Gee, i don't have the money for all of this, but i really really need that (insert ridiculous item of choice here)"? Most of America. But i digress. Marijuana.
(Note: I don't smoke marijuana. never have. never will. . . . well, maybe if it was legal. ha. just kidding. but seriously though, i'm kidding. mom, seriously, i'm kidding)
These are the pros i could think of that may or may not happen due to the legalization of marijuana.
1. reduce numbers in jail, in turn saving tax payers money.
2. make marijuana a taxable product, increasing tax revenue for the u.s. government, and in turn funding there evil plot to combine canada and mexico into one country.
3. drug cartel's power in the u.s. would be diminished until they changed products to smuggle.
4. (this one i heard somewhere else) hippie's would have nothing to talk about, which would definitely be a good thing.
5. there are definitely more, but i just can't think of them off the top of my head.
6. increase sales of food. more money into the economy.
Here are some of the cons i could think of.
1. hard, if not impossible for cops to detect if someone is high on marijuana (curt, you can correct me if i'm wrong) therefore making it hard to stop people from driving while under the influence of marijuana.
2. probably an increase in driving deaths due to the drug, although not a certainty.
3. decrease productivity at work.
4. I really can't think of too many cons although i know they're out there. I think that more of the unforeseeable consequences would fall into the "cons" category and that no one would see them coming until it was too late.