You want a network administrator to know what a routing table does, a C engineer to know basic pointer arithmetic, a web developer to understand URLs, and so on. Yes, those are all things that can be (and have been) learned, but if someone applies to an aforementioned position without that knowledge already, massive red flags should go off for all kinds of reasons.
I've listed very basic knowledge, but the same goes for more deep knowledge in a particular field. The question here is about finding the line that is still useful. Categorically saying that no such line can be found because no question is basic enough to serve as an early filter is not useful to anyone, including the candidate.
I do care if someone cannot solve FizzBuzz, because it's so bloodily excruciatingly simple that if a candidate cannot solve this, please take some time to learn the basics of your craft before wasting your own time with interviews.