Without moral agency there is no moral existence at all. See, if all we are boils down to being “a very complex hammer,” then ALL we do is merely necessary. There simply is no moral meaning to a hammer hitting a nail–or your thumb! The hammer is not morally bad for hitting your thumb.
The hammer simply doesn’t exist as a moral agent! It is not something to act, it is just something to be acted upon. It’s not a morally bad hammer for hitting your thumb–it’s just a hammer, impelled by previous forces in a never-ending “turtles all the way down” infinite regress sort of pseudo-explanation.
In a similar fashion, if all WE do is merely metaphysically necessary, there is no moral meaning to our actions at all. I just do what I’m “programmed” by experience to do, and there is no moral aspect to it–no “right” or “wrong.”
So maybe I’m Pol Pot or Stalin or Hitler, but what those folks did is not morally bad, it is simply necessary–just like the hammer doesn’t “choose” where to strike, their actions were impelled by other, previous causes and thus not morally wrong at all. They are just a complex hammer. I may prefer or not prefer their actions (in au courant post-modern style), but there is no moral meaning attached!
That also precludes knowledge (except of the most banal and meaningless type), but I’m not going into that here. But it does.