Forum Nazis

Why do forum moderators always feel like they need to stamp their authority when there's no reason to?  Users don't get paid to post messages, we do it usually to help other people and have a debate.  Unfortunately I've recently encoutered a sudden bout of forum nazi-ism on a few forums, where a moderator has shut down discussion and/or deleted posts with no obvious reason that I can see.

Stack Overflow seems to be the worst, presumably because there's thousands of wannabe moderators.  They're very strict with the rules (especially with what can and cannot be asked) and if you dare to ask something that's not allowed (or seemingly not allowed) you will be downvoted and your question probably closed.  Do you need an online compiler since your computer is too slow?  Then go somewhere else.  Are you a beginner at programming?  Then go somewhere else; answering easy questions is beneath them and you'll just get downvoted, along with a few unhelpful comments.  (It's interesting to note that often the questions that are closed as being "of-topic" usually get high votes).

Even the normally friendly World of Spectrum forums seems to have acquired a forum-Nazi.  I recently posted a link to a BBC article about the doomed ZX Vega.  The next day I couldn't find it.  I posted it again, also mentioning that the original seems to have disappeared.  I got the terse reply saying "It's been moved", and that discussions was closed, making me unable to reply asking why or where to.  Why close it?  Is WoS running out of disk space?  Or is WoS somehow linked to the shady goings-on with the Vega?

And don't even think about posting to the Subreddit "Explain Like I'm 5" without prefixing your title with "ELI5:", or your post will be deleted immediately by a computer.  Presumably it's beyond the job of a computer to automatically do this, and they'd prefer to get humans to do it.  I don't know why they feel that their subreddit is so important the posts need differentiating from all the others.

Moderators are often required for when arguments get out of hand, but unfortunately, some of them seem to feel that a moderator's job is to control the discussions, or even just create arbitary rules to give them a sense of power.