Many come here to ask questions and are often treated as though they should already know or how dare you ask...
I don't read every single post, but I can honestly say that I have never seen this happen.
What I have seen, is that someone asks a very rudimentary question and they get the answer that if they had spent just a few seconds searching, then they could have found the answer for themselves. That's very different from "you should already know." And depending on how it is worded, it is not necessarily a rude answer, either. Basic forum etiquette dictates that you put in at least a bit of effort yourself, before you demand that others expend effort to answer your most simple of questions.
Then, too, I've seen people ask questions that don't really make sense, or are kind of off-the-wall (can my family of six and I comfortably sail around the world in our Macgregor 26?). These questions sometimes get a very blunt answer. That, too, is a completely different thing than "you should already know."
Again, this may not be the very most friendly forum that God or man has ever created, but is far from an unfriendly place.