Well, very often I will click through to SO from Google to a closed thread that got downmodded like crazy, but that nevertheless exactly solves my problem in less than a minute from the first answer.
Perhaps on some level SO knows this, and also knows that their mods are perhaps somewhat overzealous, and therefore has adopted the current state of affairs as a sort of compromise/duct-tape solution.
I too, have found so many downmodded questions to have the exact answer I needed for a particular problem. It's by far the most frustrating part of using Stack Overflow.
The overzealous modding has had a chilling effect on my desire to ask a question on SO, because nobody wants their question to be downmodded as a stupid or pointless question.
It would be quite interesting to know which topics you find this happening. I don't tend to see this kind of toxicity on SO. I'm frequenting C# and .NET. Maybe Jon Skeet drags the C# community up to his level!
The overzealous modding is a feature not bug of SE sites.
I find some of the moderation really frustrating but it's worse when the people closing threads and answers are also the ones leaving zero-content comments.
They're welcome to set whatever rules they want for what's "on topic" or a "good fit". Their site, their rules. No harm, no foul.
It's just irritating as hell to waste your time clicking over there from a Google link and finding a closed discussion at the other end.
Telling Google to not index a topic would be a minor tweak. If they've found the discussion unworthy, why do they want Google to index it anyway?