MDMA is much more potentially dangerous than those other drugs, especially in an acute way. The "safety factor" (ratio between dangerous dose to useful dose) is huge for THC, LSD, mushrooms, DMT, K, etc., and much smaller for MDMA, Meth, K, opiates, coke.

There are a few (DOB?) which have safety factors around 2-4x, which is really unsafe.

erowid.org is probably a much better source of info on this topic than hacker news, though.