I have to admit, this is a tough question for me. As a law enforcment professional and ordained Christian chaplain (perhaps that lends me some moral cred, who knows?) I think I have a pragmatic approach to the problem. It may be a bit libertarian, but I don't see that as a bad thing. First, I haven't partaken of the herb for quite a long time, 1986 I think, parked by Taylor Pond with my girlfriend and a joint that a friend gave me. Second, I have spent nearly my entire adult life in criminal justice. Third, I don't think smoking pot is necessarily a good thing or a bad thing. Context of consumption is key.
From a criminal justice perspective: in nearly 30 years in criminal justice I can say with certainty that I have NEVER wrestled with someone who was stoned. Drunk? Yes. High on crack? Coke? Benzos? Tripping on acid? You bet. So, from that perspective, I don't see smoking weed as being the public nuisance that some, who I would argue have no idea about it other than what they have read, think it is. It may not be the healthiest choice for an individual to make personally, but I don't see the threat to the public, for the most part, as anything other than hype.
From a personal perspective: I have a good friend who is a paranoid schizophrenic. He has been on every psyco-tropic drug for the condition. He doesn't take any of them. He smokes pot instead. Why? I'll let him answer: "It's the only thing that quiets those demons in my head." Nothing else worked. They made him depressed, hopeless, and suicidal. I cannot argue with his logic, or the results.
From a theological perspective: well, I have to be straight up honest. In most cases, I think it's probably a sin. Indiscriminately killing brain cells and fogging your cognitive ability just for kicks is the same as getting stupid drunk. However, my Christian faith tells me I am accountable for MY behavior, NOT the behavior of someone else. What someone else decides to do, theologically, is between them and God. It's not really my business, unless the behavior affects me or my community in a negative way.
I know various arguments will be made about this, in a whole bunch of different directions and perspectives. I find most of the opposition to legalizing marijuana hypocritical. I know from professional experience that alcohol is responsible for more crime (domestic assault, manslaughter, disorderly conduct, crimes of passion, etc) than marijuana. It's not even close. I hear no objections about THAT being legal. When I do, you can try to convince me that pot should be illegal, too. For now, I think this issue is best left for communities to decide, instead of enforcing a sweeping ban decided by people who won't be affected by it. That's my opinion, I welcome yours.