Google uses Google Moderator very frequently. IO questions are filtered with it. The Android team makes public hangouts every week and answer questions filtered by moderator. I've even been in a dart hackaton where the creators of dart would answer questions filtered by moderator.

I don't think I've ever seen a bad question embarrassing the speaker after being filtered by moderator. The closest to that is sometimes the speaker will just skip the question. Since it's much more impersonal, it doesn't feel rude.