I can see you guys are trying to deny it since you're already addicted to marijuana.
Marijuana and tobacco are equally bad, Marijuana is slowly kills you mentally while Cigarettes slowly kill you physically.
Sweet.
Let's get started by observing a simple graph.

This graph isn't a
great resource because it's far too generalized as far as addictive potential goes, but it does help my point. Since these are so generalized, it's obvious there's a large difference between cannabis and ethanol in addictive potential. Think of all the people you know that drink alcohol. Then, think of how many alcoholics you know. Maybe one or two, unless you belong to your local AA group. Now, cannabis is far less addictive than alcohol. In fact, it's not physically addictive at all. Any addiction to cannabis comes from psychological addiction. So this means, in the case that cannabis were as widely used as alcohol is, you would know fewer cannabis addicts than alcohol addicts. This means you'd be lucky to know one. You happen to be pointing out many users in a thread as addicts. This is not merely statistically unlikely, it's almost statistically impossible.
Okay, so now that we've cleared up addiction, let's move on to physical harm. Actually, there's not much to say. THC, CBD, CBN, and THCV are the main active ingredients of cannabis. Since you said it kills you mentally, we're going to focus on these since the others have no mental effect. Now, in reality, there's far too little CBN and THCV in cannabis to make a difference, but we'll pretend they are in equal proportions to prove my point.
Let's start with THC, the big one almost everyone has heard of. THC has never caused a death when smoked. Ever. That's a good point to bring up. Let's quote some sources here, to assure you I'm not flinging stuff at you.
http://en.wikipedia.org/wiki/THC#Studies_in_humans Yes yes, it's Wikipedia, but if you want to argue about the validity of Wikipedia that's something for next post. It's valid. Try to find one bad thing in that entire section. One bad effect. It improves every disorder they tested it on. I'm trying to find some little bit of information on it's toxicity so that I can use this insignificant number to prove to you how little damage is done, but I can't even find a statistic anywhere that shows any detrimental mental effect. Anywhere.
Let's move on to CBD, the next most prevalent chemical in most cannabis strains. "Medically, it has been shown to relieve convulsion, inflammation, anxiety, and nausea, as well as inhibit cancer cell growth. Recent studies have shown cannabidiol to be as effective as atypical antipsychotics in treating schizophrenia. Studies have also shown that it may relieve symptoms of dystonia." We're not talking about medical use though. So we'll pretend all those schizoids don't exist. Essentially, this chemical is an antidepressant, anxiolytic, neuroprotective. I want to focus on the last one.
http://en.wikipedia.org/wiki/Neuroprotective This is a neuroprotective. Your argument is that cannabis destroys your brain. Your argument against CBD is absolutely nullified.
There's much less information about CBN and THCV available because they're so minute in quantity that most people have never heard of them. Essentially, CBN is a weak receptor agent. No real studies have investigated it's neurotoxicity, but it's a cannabinoid so in comparison to other cannabinoids it's pretty safe to assume it's not dangerous. THCV blocks the effects of THC, ironically, but not much else is known about it. It's not considered a threat by anybody.
So lets see, a quick recap. THC and CBD are both neuroprotective, disease relieving, cancer killing cannabinoids. CBN and THC are minor chemicals that people don't consider a threat. Together, on the leaves of Cannabis Sativa or Indica, 'cannabis' is not very addictive at all. Less addictive than caffeine, actually. So I'm going to ask you to make another dumb statement, that way I can hammer your sheeplike head into the ground once and for all.