I don't blog, probably, never will. I've read a few blogs, but none consitently.
I agree, that they provide a unique alternative viewpoint or a dissenting voice. Lantec is right; it is much like that quote about opinions. While a great deal of blogging might be ranting there are unique voices amidst the noise. It's got the good, bad, and ugly. It's just another outlet for expression, like Youtube etc. Sure there are alot of sad idiots goofing off on there but such is life, and such is human nature. At least, unlike mainstream media, everyone gets the opportunity to have their voice heard.
The ability to express yourself online, instantly, is a powerful thing. To be seen, heard, and read around the world can be a great opportunity to affect positive change, enlight, inspire, or just make someone's day a little lighter. In the right hands, with the right attitude and responsibilty, blogging could be a positive movement. However, this is not Utopia and some people DO have too much time on their hands.
Ultimately, it's just about hearing what people have to say, and this is where it's similar to mainstream; you can listen or navigate away. To me, blogs are just like every other form of news/entertainment/etc., they're out there, and so long as I don't bother with the crappy stuff, it doesn't bother me.