@Etruscia,
Announcement: after the age of 20, the human brain has stopped growing sufficiently so that THC and other cannabinols are incapable of doing permanent damage. THC works indirectly in your brain, causing a feeling that your brain is naturally capable of making (ever smoked weed in a dream then woke up?). Our brains are not only ready to take THC, but some extreme evolution theories argue that weed evolved into our minds as a result of millenia of regular weed use as a mystical drug (like peyote, ayahuasca, etc.).
In other words, if you're old enough to drink in the U.S. (which will always cause 'damage' above a certain concentration), you're also old enough to be unaffected by taking in THC. Smoking is, obviously, not good for you, but the tar in weed smoke is much less adherent than tobacco tar - this is why tobacco smoke smell stays for years and weed smoke stays for days tops. That means your lungs absorb less tar from weed than tobacco (by a pretty big factor, too).
The reason people get dumb from smoking is either
1. They're always high
2. They started smoking a lot at an early age (15 or younger)
3. They always have a baseline level of THC and degenerates in their system.
I've been smoking every day for the last 35 days and I suffer no more unwanted side effects than a little fatigue and some tiredness, but nothing a little coffee can't fix. I wake up spacey-headed sometimes, but once a gain a little caffeine and a few hours and I'm right as rain.
Oh yeah, the reason potheads seem dull all the time? They don't care what you have to say.
Regardless of my opinion and the evidence I use to back it up, more often than not the personality of someone to begin with has more impact on their changed personality due to smoking, drinking, whatever, than the drug does. Some drugs change everyone the same way (heroin, crack, come up with the rest) while others change everyone differently (alcohol, weed, acid, shrooms). Some are "harmful" while others aren't, but if you're allergic to weed and not alcohol then weed is more harmful to you. The human body is a huge, ever-changing, extremely complex chemical reaction that we've barely begun to understand, and it's almost impossible to say one thing is always this, another is always that (other than, say, and axe wound, or a bullet hole, serious things). Other than a few common denominators like water, carbs, and protein we're all different, and as such we all deserve different choices on altering our own body chemistry.
I'm not a thrill seeker (other than driving fast, but wup-dee-do) because I'm not athletic enough to trust my body to perform. Etruscia doesn't get messed up for fear of mental harm, which means s/he enjoys his/her current state of mental function and doesn't want to change it.
Nobody has ever died just because of pot. Not an overdose, not a case of lung cancer from weed alone, nobody. Alcohol kills thousands a year by overdose alone, and liver cancer sucks bawls.
