Blocking internet ads is no different from switching TV channels or not watching a commercial channel al together, not looking at adverts in print newspapers etc.
I think the closest analogy is nipping to the loo while the adverts are on telly, or getting your electric monk to record the programme and skip them automatically.
The only real difference on the internet is that it's practical for the advertiser to detect that you're doing it, and withhold the associated service.
Whether it makes a tangible difference to the advertising provider depends on exactly how the advertising is paid for. If they get a flat fee for sticking a banner on the guardian website for a month, it doesn't matter if you block it. If they get a fee for every hit of the jpeg, then it doesn't matter if you don't render it, as long as it's downloaded. If they get a fee for every click through, then it doesn't matter if you gaze at it hypnotically and deeply incorporate their brand identity into your psyche if you don't actually click on it...
A friend has carefully manipulated YouTube's algorithm into showing them adverts they enjoy (clever arty videos and show-and-tell of interesting products, with instrumental soundtracks). I think there's some scope for people being a lot more tolerant towards advertising that isn't actively obnoxious, but that requires advertisers not to go for the easier option.
