In many cases it's a lot of effort....and as a professional researcher I'm normally pretty good at finding things. And the logic of your position is that no one can ever ask a question that has already been asked and discussed.
Rather than simply saying - 'seek (via the search facility) and ye shall find'....the really helpful thing might be to point them in right direction and provide a link (as some do) to the thread in question.
Personally I don't mind 'repeat' questions..I can always choose not to read it, but even when it is going over old ground, there might be something new to learn. If we hadn't asked questions (most of which must have been asked before) when we bought a boat and first joined two years ago then we would have been up the K&A without a mooring! Yes, OK, it can be bit bruising on here sometimes, but I've learnt a hell of a lot, and have tried - when I can - to give something back.
Edited for typos