The Germany of today is the legal successor of the third reich and that cannot be discussed away. It is a fact. And that is not even going into moral obligations stemming from that.
If people confuse historical responsibility of a nation state with their own personal responsibility then that is exactly the kind of dangerous nationalism that leads societies straight back into fascism.
maybe they reject it because they weren't personally responsible for that stain. Not saying the stain doesn't exist, but don't you feel it's kind of unfair to be born German if you have this Erbsünde and thus aren't allowed to...