Yes. It's good to evade a predator. And the process you describe is accurate. But it occurs because the first elephant without tusks happens to live a longer life and prosper and left a large number of descendants just in time when they were hunting by their tusks. It just occurs, it's not a response in the sense of the specie but in the sense of the randomizing events we call world. That's why I said OP is, in the core of his argument, right.