usenet had its weight (or wideness) and freedom, (no moderetors no drivers how it can look like just a place for posting and tematical hierarchy it was/is good, Im sad it lost popularity)
Usenet had moderated newsgroups, which required approval before posts went active, but don't assume the rest wa an anything-goes madhouse.
The non-moderated newsgroups were semi-moderated with cancel messages. Individual sites and various groups were granted the power to cancel messages, causing them to be obliterated on the server, to stop propagation across the rest of the network, or both. Many location still use automated cancellations, such as when binaries are encoded as text in a non-binary newsgroup. Spam filters are also implemented with cancel message, but usually have a pretty low threshold.
I don't see what you are complaining about; a quick Google search says there are about 20,000 still active non-binary usenet groups out there. And as I mentioned, both comp.lang.c and comp.lang.c++ are still active, both listed in Wikipedia's list of most-active usenet newsgroups. You can still get that feeling if you want it, just point your news client at either of those, or whatever else you think you want to view.
Same seem to be with irc? Is irc in total decline now? Or are there some servers or somethink where I can connest and have 50 - 200 people in one room?
Again, there are islands of popularity. Yes, go find some, if that is what you want. Channels like #C are much smaller than they were in the '80s and '90s, shrinking as #C++ and #Java and #C# grew, but you can still find quite active irc channels out there, too.