I agree but MDMA is not comparable to marijuana or hallucinogens. It is structurally similar to amphetamine and there are studies suggesting that it causes brain damage even after a single use.
People have been known to commit terribly violent crimes due to MDMA. It's not the standard effect it has, but it happens enough to remind me that it's an amphetamine.
No, you're confusing correlation and causation. MDMA users have been known to commit terribly violent crimes.
Besides, alcohol users have also been known to commit terribly violent crimes (and unlike MDMA, which is near impossible to study in the US, we've studied alcohol enough to know that it is in fact a contributing cause of violence). The point is that it's hypocrisy to allow one clearly dangerous substance to be used by the population and to make another one illegal.