Let's simplify this, knives are not and never were the problem, craptastic divers are and always have been the problem. I do an awful lot of diving and nobody I get in the water with ever pulls their knife out unless absolutely necessary. It's a stupid law, babysit the crappy divers, don't punish good divers.
Many people found prying off a piece of coral to be absolutely necessary...I don't think we can get much clearer than that.