PWOARH! Big socks your wearing there.
http://en.wikipedia.org/wiki/Long-term_effects_of_cannabis
Nuff said.
Ok, so looking at your evidence the very first sentence of the article is "Though the long-term effects of cannabis have been studied, there remains much to be concluded". Before delving any further, I need to really emphasize the fact that both the good and the bad LONG TERM affects of cannabis have barely been studied and as such there remains much inconclusive evidence about it.
So let's look at the long term (well known and well documented) effects of Cigarette usage:
http://en.wikipedia.org/wiki/Health_effects_of_tobacco - Using wikipedia just like you did for Cannabis, there's a huge host of well documented and known diseases directly related to cigarettes - cancer of like 10 different organs, bronchitis, heart disease, strokes, emphysema, loss of limbs, heart disease... and the list goes MUCH further. You also don't need to be a pack a day smoker to get some of this crap - you can smoke like 1 - 3 cigarettes a day and if you're unlucky a year or two later have some serious repercussions.
In terms of Marijuana, there is a loose link to psychosis based on a few studies. Nothing solid enough to draw a direct link to marijuana with. However there is also a large amount of debate (as from your wikipedia article) on whether or not this is a correlation or causation, so again, MUCH more research needs to be done to produce anything solid. Many people who develop psychosis have had it in their family or already have exhibited symptoms of the disorder, so it's very hard to point to marijuana as the cause of the disease - rather evidence suggests that at most, it's a factor if you're already starting to develop the disease. You don't have to smoke cannabis to ingest it, however smoking is obviously bad for your health in any way - however the respiratory effects of smoking cannabis are quite clearly less than cigarettes.
Now you'll never hear me go out and say "cannabis is good for you", "you'll be fine no matter how much you ingest" etc etc. That's at least in my opinion, rubbish. I think it's common sense that too much of something that affects your brain would affect your mental ability in some ways . I do know people who have smoked lots of cannabis and become very slow and generally dumb, with that said I know someone who smoked cannabis almost daily in Year 9 - 10, stopped for year 11 - 12 and pulled off a 99.90. All of this however is anecdotal evidence so don't presume that it's factual - just like you know people in St Albans who are dumb stoners, we simply can't draw conclusions based on our own personal experiences, rather just use them to guide us in making our own decisions.
There has also been some research on Cannabis being useful in negating pain in people with permanent debilitating conditions, alongside some research into its affects on the brain. I think if you googled it you could find some articles on the research, marijuana (like Morphine I guess) can be abused, but is also something we should not be dismissing in terms of potential medical benefits. More research is definitely needed. I also feel the need to comment on addiction - Marijuana is much, much less addictive then cigarettes. People who smoke weed all the time generally do it because they love the feeling, not like cigarettes where you actually start craving the nicotine hit. So I think that's another reason why weed is better for you than smoking - you're less likely to get hooked on the stuff.
Anyway, if you asked me if you should legalize Marijuana I'd say yes - not because I think we should all be smoking it, I don't touch the stuff and wouldn't want any kind of drug affecting my brain in the VCE years (except maybe alcohol hahaha). But if you asked me what I thought was better, people smoking cigarettes every day or people smoking weed every day, I think all the evidence and research (or lack thereof) points to the fact that Marijuana would be better for you especially in the short term. Like Russ said, 1/3 of people over 13 have tried Marijuana, and really there hasn't been ANY research that has shown that occasional usage of the substance (i.e. once a month) will lead to significant loss of health.