I'm a happy user of StackOverflow community, I highly participate in Java Q/As mainly by answering questions. After seeing this thread and similar questions on Meta StackOverfow[^] I start thinking on what can possibly be the root of all evil (like premature optimization ;P ). Anyway, let me try to provide a personal opinion on all the topics covered in your post:

Quote:

if a new one asks a simple question, then the top users starts down voting, ranting

Define simple question. For example, if somebody in Java asks "how can I create a hello world app" then I would post a comment saying "that's covered in a tutorial" and vote to close. This question lows the quality of the site. Ok, another (not that) simple question: "this piece of code doesn't work code that doesn't even compile I appreciate your help." ok now this is unanswerable at all, first because the code doesn't compile, and if it does compile but there's no stacktrace, then I usually have to read through a wall of code to tell OP: "you didn't initialize foo variable, thus you getting a NullPointerException...". There goes another simple question that lows the quality of the site. And a last example of a simple but too broad question: "how can I create RESTful web services in Java?". Again, this is an unanswerable question that can is already covered in plenty tutorials. No need to reinvent the wheel in stackoverflow.

Quote:

If someone don't have knowledge on particular topic or another then the regular users start insulting them.

I'm ashamed of this, and I see stuff like that for one of the following reasons (AFAIK): - OP is really lazy to understand the answer. You spot a question like "how can I foo the bar" then an answer posts "Use quo, it will foo the bar as you expect: Here's a sample code fulfilling the answer" and I upvote it for showing a good example, but then OP raises a comment like "ok now I need to baz the bar from foo, how can I do that?" and I reply in a comment "OP please read about how foo and baz are very close you just have to change one line it's not that hard" and OP starts complaining about me insulting and giving him the bad eye. Then, another user reads all that and provides a new answer with the line to change and he gets the accept