If this were the case, newsgroups would be very boring indeed. Whenever people come together for any length of time, or when they share in a common goal or set of beliefs, they form a community of sorts. When communities are disrupted, people get annoyed. People get involved in their community and thus have a vested interest in keeping it the way they like it. It is bad because it can alienate outsiders, discourage them from joining the community, and even cause out-right hostility towards them.
History is littered with such occurrences.
SPAM SPAM annoys us because it breaks the sense of community. Television advertising also annoys most people, because it interrupts their favourite show or the Saturday night block-buster movie. Some of us put up with TV advertising because it means we get to watch TV for free. Many people, of course, prefer to pay for their television without adverts. With SPAM, on the other hand, we pay to receive adverts.