That's really it. Everything it does is geared toward that, and it does it quite well.
I have lots of SO points. A lot of them have come from answering common, basic questions. If you think points exist to prove merit, that's bad. But if you think points exist to show "this person makes the kind of content that brings programmers to our site and makes them happy", it's good. The latter is their intent.
Does having easy answers available on SO make us dumber? I doubt it. People have made the same argument about search engines, and you probably could have said the same about encyclopedias.
Yes, and that is an incredibly valuable service.
I haven't participated in StackOverflow actively, neither asking nor answering questions, for various reasons, some perhaps related to some of the OP's complaints, but it has saved me many hours of searching through documentation and mailing lists just by being there.
I suspect the contribution to global programmer productivity is enormous. It's true that it may tend to reduce the amount of very detailed knowledge about very narrow topics that people need to memorize but I think that externalizing this type of knowledge is the way to go. As long as your mental models about the basic workings of the software you're using are essentially correct I don't think there's much harm in depending on external resources for specific details.
if SO manages to loose this community then signal to noise ratio will further increase, the site will go down the drain and new competitors will appear.
Are people really that motivated by points and badges? I think these are similar to toy money/monopoly money. if a person does not like the process of investigating a problem then this will not be a sufficient motive for participation; if its not fun then nothing will help here. Career incentive? I doubt that, for a real job they will look at other things.
Still SO has a dilemma, like wikipedia it is a huge amount of text and it needs some meta moderation, and then some meta meta moderation too; so monopoly money is probably supposed to move a person up along this hierarchy. The problem is that a hierarchy of moderators will eventually piss off at least some competent contributors, if not all of them; this problem is common to most sites: slashdot, wikipedia, SO, HN - over time they all run into this problem.
Its like in real politics; nation states need bureaucrats, but these can also turn into a mortal danger to the state
Yes, in that the worlds largest helper only supports simple boring common questions, as per the article. If you're trying to do stats in scala, and the only help you can get is "hello world" in java, that's not good for Scala, statistics, or much of anything else, making the world overall dumber.
By analogy, lets say reality TV shows completely push video documentaries off the air. This is not so far fetched. The net result is likely to be dumber.
Are people posting Java "hello world" answers on your Scala questions? I doubt it. Are you manually slogging through dozens of Java questions looking for Scala ones? You should be searching.
I see no reason why you should ever have to look at Q&As irrelevant to you.
Worst case: you have questions nobody can answer. Which means one of two things:
1. Your question is unclear or too specific to your situation
2. You're working in a niche area.
If #2, you're no worse off than if SO didn't exist. So what's the problem?
"The proposition would seem to require the assumption that all programming can be reduced to cookbook recipes."
Its one of many effective ways to start learning a language, although not the only way. To distort or screw something up, you don't necessarily have to mess up 100% of the population, just a good chunk of them. You could try to argue that few to no experts ever took their first steps as cookbook script kiddies, but I don't think that would be successful.
And you seem to mistake knowing languages for understanding programming. The essence of the skill is the ability to formally specify an algorithm which solves a given problem; the rest, more or less, is libraries and syntax.
Now people are starting to hate SO, for very different reasons. At last! They've become the new expertsexchange in every way.
 https://en.wikipedia.org/wiki/Experts-Exchange 4th paragraph.