This is a tricky answer choice. It is not that there is purely a generalization in the passage but rather that this sentence places a limit on how broadly we can apply the conclusion in general.
The conclusion is that the recent humanizing of vampires is unfortunate. But then the sentence under question says that usually this is a good thing. So in fact, what this sentence is doing is saying that the humanizing of vampires in this case is unfortunate but the humanizing of other evil may often be good.
I hope this helps. Please let me know if you have any other questions or would like me to elaborate further!