Also, just because someone goes to the emergency room doesn't imply something is wrong. Merely that the user thinks something is wrong. Think back to the first time you got high and you may see why. People get worried and paranoid, though there may be no problem at all.

Smoked Marijuana: is Mutogenic, Fetotoxic and Carcinogenic - can Impair the Immune System, break down the Male Genetic Code and Injure or Destroy the Eggs in the Ovaries - can cause Bipolar Psychosis, can trigger Schizophrenia, can Slowdown the Brain's Energy and can be a co-factor in producing full blown AIDS in HIV patients.
So many people have smoked marijuana for so long, if any of that were true why hasn't the human population suffered a population drop? Think of how many of your parents and friends parents smoke marijuana.