What's kind of interesting is a lot of the target SO questions are implicitly opinion-based. For any "How do you do X" there might be multiple ways to do it so the question is actually "what's the best way to do X" which is up for anyone to interpret "best". And this tends to work out nicely, you'll often see multiple answers where the top upvoted one is not the selected one, or some answers build off of other ones and describe why they think it needed updating. This kind of nuance and seeing multiple, competing answers is often pretty helpful while you're learning.

Plus some of the best, most interesting questions on there are "community wikis" which often tell you they should have been flagged as opinion based but are preserved for historical significance.

Because of that I really don't see the point in being so dogmatic about closing opinion based questions. Even something like "emacs or vim" I can imaging being a useful question, with a highly upvoted, thought provoking answer arguing each side.

The historical significance thing is particularly annoying. It's an explicit statement of "We want this type of content, but the system of rules that we created and can change any time we like does not allow this type of content, and what do you mean, 'that seems like something we should do something about'?"

"how to do X" has an objective answer: "here's how". Whether it is "the best" is subjective. That is why multiple answers are allowed on Stack Overflow (instead of a single article as on Wikipedia modulo different languages).

The accepted tick on the answer says that "here's how" might have worked for the question author.

The most upvoted/popular answer works as a rule (there are exceptions). Popularity contest is not the best way to get the truth on a technical subject but it works more often than not (you can read the answer in the chronological order if you like).

> Some questions are closed because they require opinion-based answers ("What's the best ...?", e.g.).

The problem with this is that there are opinions and preferences and biases (and so on) hiding all throughout even the most (seemingly) objective questions and answers. The SO folks think they're making a more meaningful distinction here than they actually are.

Not to mention "what's the best <X> library" can frequently be answered in an objective fashion, if the answers give a breakdown of why.

Things like "lib A requires excessive boilerplate compared to lib B, see example", or "lib A can't be installed under the following platforms", etc. What should be voted down on those types of questions isn't the question, but poor answers.

It's really frustrating, because getting the opinion of experts who have tried a bunch of alternatives, and know the pros and cons that matter, is exactly why I go to SO frequently.

What's stopping them setting up an opinions.stackoverflow then if they've already got sibling sites? Somewhere to contain all of the opinion-based questions.

They do have some. For example the Software Recommendations Stack Exchange:

http://softwarerecs.stackexchange.com