This info may be usable to those who have never used Stack Overflow (programming Q&A) / Stack Exchange (every other subject) (which I will refer to as SO and SE respectively from now on) or haven't used it for several years. Here's what happened to it and why you should probably not waste your time posting there.
By the way, this is not a rant, I stopped going there years ago and I'm not the kind of person who would hold a grudge for years and bitch about it in another community. Take this for what it is, a warning.

First of all, every community on the internet has the same issues. Reddit, Tumblr, Phpbb and similar forums, Facebook groups, Quora and anywhere where you can ask and answer questions in a specific "community". Everywhere there are trolls who just get thrills from annoying you, there are competitive people who consciously or subconsciously want to win an "argument" even if there isn't any, negative people who interpret your posts the wrong bad way, people who like to spam, people who intentionally or unintentionally derail your topics and end up wasting your time, moderators/admins who have an ego issues or who do not do any kind of analysis and mediation of the situation and equally penalize two people arguing or don't punish any of them including the wrong side. These issues are everywhere because these are negative aspects of the human nature.

The extra problem SE/SO introduced and why I believe it is digging its own grave is this, which someone else described much better than I could:

It really annoys me how people on StackOverflow are more interested in keeping their house clean than actually helping people.

And that's all there is to it. Anything else is also common in any other community, but SE/SO added another serious issue by having the goal of being a Q&A site rather than a discussion site where people could search for an already asked question with an answer rather than asking the same question was doomed from the start, because ordinary people where given the task of deciding whether a newly asked question and a previous question by someone else from the list were the same or not and whether the question was a question or a discussion. No matter how good a moderator is this is often subjective and debatable, so in the end so many questions were unjustly closed or downvoted without giving the OP the chance to discuss that with the moderator that they ended up alienating new users.

So basically SE/SO ended up taking itself too seriously and it's goal of being an existing list of questions with answers that they "were more interested in keeping their house clean than actually helping people". The system's goal was to help people by having a list of questions but it shot itself in the head by making it difficult for people to add more questions to the list and get help.

Of course in the complete opposite of the spectrum, spam filled 4chan-esque communities are no better but I feel like SE/SO was very close to finding a good balance but went to the other extreme.
The site is still going to live on just due to the sheer number of questions and answers available to be used but I don't see it as a good first place to go for asking for help anymore, because there is such a high chance a moderator will decide your question is similar to another one or will consider there is no clear answer to it and there is a discussion to be had than an answer posted and close it that there is a high chance you will have the long post you just wrote closed without prior warning that you’re better off asking it somewhere else such as reddit or forums and only take the risk of offtopic comments, trolls or other issues I mentioned.

Just my thoughts.