A Question About *SPOILERS*

Why do so many posters need to put a Spoiler Alert on topics in the IMDB boards? There are plenty of places to read reviews about movies including the first page that comes up on IMDB. Why would someone go into a discussion board about a particular movie and not expect to find out key points about it? It seems that if someone values their entertainment dollar then there are plenty of places to go for reviews of a movie besides a discussion board. I've seen people get quite upset when something they consider a spoiler is mentioned during a discussion about a film. If a person attends a film class about Hitchcock they should expect to find out certain plot points in some of his movies they might not have seen. Of course I might be looking at this in a wrong way so I am open to any different opinions. I would like to hear what anyone else thinks about this.