Lately, there has been many atheists trying to promote the legalization of marijuana as soon as it was publicised that it didn't have many (or any) physical problem associated with it. Whether it's safe to use or not, I don't think legalizing in public is something we should do.
Firstly, if it is being smoked, then everyone around you will also be doing the same (second hand smoking). People with delicate lungs (eg: emphysema) or sensitive senses (eg: Autism) may end up having problems with others smoking this in public. If marijuana were to become legalized, then it should be eaten or drunk instead of smoked. This is technically the same issue as cigarette smoking in public
Another problem associated with this, is that even though marijuana is 'ok' for you, the smoke itself and not the chemicals in the smoke is what is bad for you. Let me explain; our lungs have evolved to breathe in ~70% nitrogen and ~20% oxygen. Breathing in smoke is essentially ~35% nitrogen, ~10%oxygen and ~55%smoke. If this were to be breathed in for long periods of times, and on a regular basis will cause lung problems. When people say that marijuana isn't bad for you, they mean specifically marijuana, because consuming it in any other way won't give you lung problems.
Even though using marijuana may be physically 'ok' to use, there are still side effects that come along with using it. According to http://www.schizophrenia.com/prevention/streetdrugs.html, 8%-13% of schizophrenia cases are linked to marijuana. Even though this may not seem like very much, people who regularly use marijuana increase their chances of schizophrenia by 600%. This means that if everyone in Australia (22 million) became a regular smoker of marijuana, then 145200 people would end up with schizophrenia. BUT not everyone does smokes it, so the numbers will be smaller. If marijuana became legal, then we are allowing (statistically speaking) 145200 to 'obtain' schizophrenia. The population of the USA is ~300 million. If marijuana was legal and everyone became a regular user, then 1980000 people (statistically speaking) will get schizophrenia. If the numbers are lower, say 1/5 Americans become regular users, then 396000 people (statistically speaking) will get schizophrenia. (The maths for this is simple, 66/1000 users according to http://www.schizophrenia.com/prevention/streetdrugs.html have schizophrenia from marijuana use; 66/1000x(population) and then you have your answer).
All in all, the main purpose of this is to say that if marijuana is legalized, then it shouldn't (legally) be smoked, rather it should be consumed some other way.
Marijuana legalization and second hand smoke are separate issues. Tobacco is legal, yet I'm constrained by law from smoking it in certain public places and by common courtesy from smoking it in others. I'm not a marijuana user for several reasons -- 1: I had enough of it in the '60s & '70s to last a lifetime. 2: I can't afford it. 3: It would too often interfere with getting certain things done. And 4: Since I left my beloved Rocky Mountains I live in a state where it's still illegal and aggressively prosecuted. Still, I wouldn't be opposed to sharing a joint with friends in an appropriate venue. I've know people who use pot constantly, and they'd probably be better off if they used it less. And I've known people who never use it, and they might well be better off using it more.
I think that legalizing, regulating and taxing marijuana is the right thing to do for the good of society. My home state of Colorado recently passed a 25% tax on pot. I thought that a bit excessive, since it skirts a taxing level that flirts with keeping bootleggers alive. Perhaps taxes similar to those on beer would be appropriate. Colorado charges a nickel per six-pack -- around 1%, and the feds tack on a bit more. Beer can have social repercussions for excessive use, while pot largely does not, at least not nearly to the same extent. Anything much above such sane levels of taxation & control could be seen as a "Sin Tax", wherein those in a position of power persecute those who hold different values just because they can.
Regarding that, I'll leave you with a selection of lyrics from a pretty good song:
Jesus was a Capricorn, he ate organic foods.
He believed in love and peace and never wore no shoes.
Long hair, beard and sandals and a funky bunch of friends.
Reckon they'd just nail him up if He come down again.
'Cos everybody's got to have somebody to look down on.
Who they can feel better than at anytime they please.
Someone doin' somethin' dirty, decent folks can frown on.
If you can't find nobody else, then help yourself to me.
As others have suggested you should do more research to reinforce your position. But I must say you are sampling research that has not been properly vetted. What your Schizophrenia research fails to address is the correlation between those with Schizo and those who use marijuana to quell the effects of schizo. In almost every case it was found that the patient first began to display symptoms of schizo, and as a result in most cases would turn to marijuana for fear of stronger more addicting meds to treat schizo. There really is no reason for its prohibition other than bad science, government propaganda, and decades of misinformation. The science is there, you're going to have a hard time disproving it now thats its not being stifled by our government.
Or, people with schizophrenic tendencies, also tend to like marijuana.
People choose drugs that reinforce their usual habits of mind, I've heard.