A Q&A website needs both people who ask questions, and people who answer them. Perhaps the latter even more than the former. You can ask a question on stackexchange and have it answered by Peter Shor. Not having the platform inundadated by dumb repetitive questions and homework problems is the compromise you need to retain such talented people on your platform.

If you want an example of what happens to a Q&A site without any gatekeeping, look at Quora.