You can't abuse marijuana LOL!
I know kids who have died from the smoke... not the weed, but the smoke itself can kill. Although its worth pointing out that they were not smoking safetly, but still. Its dangerous.
Honestly, I know tons of people who smoke, and from my experience- not one of them is anybody. They all have no ambition in anything, and some of the ones I knew before they did pot were different. Its not a direct, instant change... you don't smoke and loose 30 points of your IQ. However, its long term effects are notable, and with every case I have seen, they are bad. People smoke due to the age-old human problem of putting short-term happiness as a top priority.
Also, there's almost no use in comparing drugs severity though, the thing is, they are all still bad.