The payment for the service is coming from the ad owners. Me choosing not to download parts of a webpage isn't piracy, it's me choosing not to download certain parts of a web page. Nobody has any right to force data I don't want onto my computer except me. Piracy is illegal, adblocking is not (so far).
This isn't like you copied a game and cracked the DRM. An adblocker just strips out the HTML and javascript needed to display an ad. It's not different than if you turned off images in your browser like we used to do back in the day on dialup to make it load faster.