Disclaimer/Context: I was the Product Manager for Ad Products at Vox Media for 2+ years
I pay for my expensive bandwidth. If you attempt to pollute the bandwidth I pay for do not be surprised if I cut out the crap you try to force feed me.
If you can't support your business that's your problem. After all, the down side from all these businesses folding is that we go back to a web when such parasitic practacies didn't exist, well that sound like a deal to me!
In a similar vein, if I take a free newspaper, no-one follows me round and refuses to let me turn the page unless I confirm that I have looked at all the ads on the current one.
noun 1. a punitive ban that forbids relations with certain groups, cooperation with a policy, or the handling of goods.
In the sense of "cooperation with a policy", this certainly is in fact a boycott. Also, a bit of a stretch, but blocking adds is forbidding relation with a certain group (advertisers).
Further, a boycott may or may not include suppliers (or any other group associated with target). For instance when some restaurant chain is being boycotted, you don't often hear "also don't buy $X apples, they sell things to the evil chain".
The point being - it is consumer activism, people are saying "I like your site, but I won't be involved in the unreadable mess that it becomes with ads popping up everywhere." That's a pretty strong message, and far more pointed than just avoiding a site. In the later case, the message is unclear... is the problem the site content itself? Is it the ads? Is it something else like the layout?