It's boring to see the same thing over and over again. If I got a new ad every time, maybe I wouldn't block them.
1. It is mostly ugly and aesthetically displeasing. I care about how things look and take steps to seek out and appreciate things I like looking at (eg art, OSX) and avoid things I don't (advertising, Windows)
2. I recognise the human brain is a flawed machine and susceptible to clever manipulation, even when the person knows he is being manipulated. Thus, I avoid any contact with known-manipulative forms of messaging whereever possible - this includes most forms of advertising. I have no such aversion to, say, movie trailers (I generally love them) or local business catalogues, etc, since they are informational only and do not try to manipulate me. By the way, if you think you're immune to this manipulation, you are 1. in the vast majority of people and 2. provably wrong.
And I do dislike excessive consumerism, especially around christmastime, and credit advertising for spurring it on - but whatever, people can do what they want.
You always mentioning this "free, advertising-supported internet" but that is a simplistic view, IMO. The price of "free" is that you are expected to view, absorb, and presumably act on, commercial messaging. There is no immediate monetary charge, no, but there certainly is a cost.
Advertising is there to tell me about products and services I didn't know about. I find that useful, and so do most people. Advertising (when done well) can be funny, witty, clever, artistic, etc. Sure, you get a few ugly adverts, just as with anything else.
I'm guessing it's mainly a "I haven't owned a TV for years/I hate consumerism/Anti-mainstream" type thing at work here...
I don't understand hate of advertising though. Are you anti-christmas presents also? Do you hate blockbuster movies? Hate disney? Hate consumerism? Maybe there's some 'hippiness' going on I just don't get.