Marijuana makes everything bad...
It's all because weed (or any cannabis) fucks your head up...
It really does turn people paranoid schizophrenics, people who may never have lapsed into that state of permanent psychosis. I have been inside the nut ward three times now (not for drugs, but for suicidal depression predating drug use). I have met a fair few people there who swear that their schizophrenia was caused by cannabis. Other schizophrenecs won't admit this, and still hanker for it, try to get visitors to sneak it in etc. And then they get more schizo.
I remember when I was a teenager, and I started having panic attacks, and it was after I had been smoking cannabis for a year or two. My first few serious panic attacks happened when I was not stoned, when I had decided to jack it in because I would always green out and panic on the stuff. I took my two little sisters to the cinema to watch Tarzan, and I had to run out of there because I thought I was going to die. Went to the hospital etc. Anyways...
A few days later, I was with this guy I always used to smoke with, and he offered me a toke on his spliff as a friendly gesture, as we had fallen out. I did, and then felt like a complete asshole. After this, I couldn't eat for days, had paralyzing attacks of depressive anxiety - where it seemed as if my soul had been hollowed out and all there was around me was pure evil. People looking at me, they couldn't comprehend. I stood there in my girlfriend's arms crying not knowing what the hell was happening to my mind, knowing I had taken a turn down a one-way road leading to all things shit. Struggling for a day to grab my breath I lay on her bed like a frightened animal, until my sanity resurfaced, and swore that I would never in my life smoke that devil's shit again.
That hollow depression that Ungoliath describes, and the paralyzing mega-rush of negative thoughts Lacey K describes is exactly what weed does. It searches out every possible dark, negative energy from the quantum possibilities of your mind, from the deepest recesses of your psyche, and shoves it all in your face so fast and confusing that many people struggle to keep on top of it and retrace the neural pathways.
Opiates and Benzos have much in common thrapeutically, in this regard; this is why you feel you must take the dope first then the weed, because dope (and benzos) put a very strong forcefield against much of this negative shit, and enable you to keep on top of it and explore the psychoactive and psychedelic space going on. The other way round, and that evilness makes you second-guess everything - regardless of how you are living your life.
Long live benzos and opiates!