I think hysteria – and fear of the unknown and different – was a main ingredient in the original prohibitions; if the slate were wiped clean and the same laws proposed now, hysteria might not be as much of a factor.
But, as others have said as well as me, once a law is passed, it is darn hard to repeal, especially if it purports to “save lives” or “save the children” or whatever.
Some people feel that if a law exists, there must have been a good reason behind it, and it takes on a life of its own. Rarely is a law passed with a sunset clause that forces reevaluation of its raison d’être after a period of time.