Of course they should. I'm sure this has already been mentioned, but the only thing that is really wrong with pot is what the drug dealers put in. The stuff they put in is usually addictive and much more dangerous than pot on its own. If it was sold legally then this problem would not arise. There would be quality control in place so as it would be as healthy as possible. However that is only if the government sold it (Which is most likely). If Marlboro sold pot cigarettes you can bet they would shove treace amounts of cyanide into them (they do that with cigarettes already). If it was the government selling the pot, then it would also be a huge boost to the economy.
And as for all the 'Gateway drug' malarky, if it was legalised, that wouldn't be a problem. I feel that once the illegal barrier has been broken after smoking weed, people don't feel so bad about doing other illegal drugs (And this is coming from experience). But If it was legal, then it would be like alchohol, they don't lead onto harder stuff (usually) and I feel that that is because they are legal.
And another effect it would have is it would remove the whole idea of a stoner group. Nobody is labeled as a 'drinker' or whatev because they drink, yet its effects are as strong as pot. People who smoke cigarettes aren't labeled because they smoke. Because its not illegal, its just something people do.