I'm against the use of drugs, including marijuana, mainly because of my own personal experiences. I don't think they are beneficial to life.
But I don't really think pot causes poverty, rather, do not poverty and other traumatic/painful life experiences cause somebody to want to ease their pain with drugs?
I think this is where the addiction comes in. When life is too much, and we want to escape, then we are trapped trying to keep this chemically induced mental and physical equilibrium. Trying to stay happy and well. And failing for the most part because what goes up must come down. The brain changes and rewires itself to crave the artificial stimulation. It won't produce the natural highs it used to. Your brain stops making serotonin, but it overproduces the little places that receive the serotonin so it produces that craving even harder.
People who just recreationally use pot are NOT the people we really have to worry about. It's the people who become addicts to alcohol, cocaine, opiates, meth, barbiturates. These are the people who commit crimes, spend their rent money, cause families to break up, neglect their children, and become unproductive drains on society.
It may well be that pot is a gateway drug. It was in my circumstance. But if somebody can stick to pot, and not use it more than once in a while, I don't see the immediate harm.