Hitler and the Nazis, intentionalists or functionalists?

In Holocaust studies there is a debate between two schools of thought. They're called intentionalists and functionalists.

Those words mean other things elsewhere, but here they mean, roughly, that 1) Hitler and his inner circle planned the Holocaust from the outset and then directed or manipulated events and people to make it happen (intentionalism); and 2) the Holocaust, while certainly both real and evil, was the end product of a set of values, goals, and forces that the Nazis unleashed but did not fully control. The "final solution" was in certain important ways a bottom-up affair, one that more and more presented itself to the leadership for authorization, commonly after significant atrocities had already occurred. And then the leadership assented, of course.

It should be pretty obvious that this is one of those debates that admits of middle positions between the two extremes. Historians of both persuasions have enhanced our understanding of the Holocaust through worthwhile and insightful scholarship. One can respectably lean either way.

But I do find the functionalist position a great deal more interesting, and a great deal more terrifying.