hard = heroin, cocaine, meth

soft = weed, DXM, adderall

legality doesn't really have anything to do with it - hard drugs are more illegal because they are more dangerous. If all drugs were legal, they would still be called hard drugs. As for the law judging what is bad for people - you just have to look at a heroin/cocaine/meth addict to see that it can fuck you up big time.