I've never bothered to try smoking marijuana, and don't have any plans to (partly because I see no benefit in it, and partly because it's still technically illegal). In my eyes it's a lot more harmless than cigarettes or alcohol, and while I believe it should be legalized, regulated and taxed, it still wouldn't make me any more likely to try it if that happened.
As for judging people that do, I really try not to. Sure, I think it's stupid when I see middle school kids doing it, but in the grand scheme of things it's none of my concern. The same goes for anyone else I see doing it- if it isn't affecting myself and others in a negative way, they can do as they please.