There is nothing vague about Usenet. It may be hard to pin down what is and isn't part of Usenet at the fringes, but netnews has tended to grow amoeba-like to encompass more or less anything in its path, so you can be pretty sure that if it isn't Usenet now it will be once it's been in contact with Usenet for long enough. There are a lot of systems that are part of Usenet. Chances are that you don't have any clue where all your articles will end up going or what news reading software will be used to look at them. Any message of any appreciable size or with any substantial personal opinion in it is probably in violation of some network use policy or local ordinance in some state or municipality.
Some people are control freaks.
You will run across them every so often. Just don't believe everything they say. If you run a news system you can be a petty tyrant. You can decide what groups to carry, who to kick off your system, how to expire old news so that you keep 60 days worth of misc.petunias but expire rec.pets.fish almost immediately. In the long run you will probably be happiest if you make these decisions relatively even-handedly since that's the posture least likely to get people to notice that you actually do have control.