if you think people over-express their opinions on blogs then why do you hangout in places like HN, click on links, read blog posts, and then go in and comment on them?
Because silent dissent is a great way to not let people know you have a differing opinion.
Well, I don't do much of #3 & #4, but do plenty of #1 & #2. I count on the community to vet the loudness of private time-wasters. And so public watering holes become more palatable.