To me it boils down to the questions of on whom does the onus fall to ensure content consumers see advertisements (or better said to ensure content consumers don't block advertisements,) the consumers or the advertisers.
I'll use this quote from Azrael to help make my point that the onus falls on the advertisers.
Azrael wrote:Unless you're in some prior wage-earning arrangement, your time does not have inherent, tangible value that you can make a claim against someone else for wasting. Think about loss-time accidents -- you can make a claim for compensation for lost wages, but if you don't have a job, you can't.
The key is the prior wage-earning arrangement. When you go on on the internet or when an advertiser makes an advertisement and pays a webpage to host it there is NO monetary agreement or even non-monetary agreement between the consumer and ANYONE. This means all parties are free to act basically entirely how they please. Advertisers/webpages can advertise whatever and however they like (even inappropriate pop ups) and consumers can choose to view or not view ads.
In light of Azrael's quote, even though the advertisers spent a lot of time working on the ads in anticipation that consumers would view those ads, the consumer is not stealing by using adblock because there was no "prior wage-earning arrangement." The same goes for consumers viewing the ads. If a lengthy ad comes up and takes up 3 minutes of the consumers time it is again not stealing the consumers time because there was no "prior wage-earning agreement."*
I think this point of view is justified by two things. 1) In principle it will in some sense be governed by the market. If people can stand and like particular advertisements those advertisements will generate revenue for the webpages and advertisers. If consumers abhor certain sorts of advertisements then those advertisements will not generate revenue for webpages and advertisements and they will be phased out of that part of the internet.
2) I was going to say here that websites are free to create a contract which makes it so users have to watch/see advertisements to see content since it is this lack of contract that permits the consumers to use adblock. However, I realized that webpages don't even need to use adblock. It sounds like they can just set up their webpage to block the content from people who are using adblock without any prior agreement which is ALSO fine because it's their webpage and they can do what they want.
Also, I think one thing to point out is that these sorts of issues are still being sorted out in real time by court. There isn't really an answer to whether adblock is ethical or not because people haven't really decided how they want it to work.** The question sort of comes down to this. With a store there is an expectation
that customers will pay for items they take out of it. If they break this expectation we call it stealing. At a dinner party there is an expectation
that the host won't use it to to unexpectedly advertise to unsuspecting hosts. On the internet advertisers have an expectation
that when they produce an ad that consumers will view it. The question is, when each of these expectations are in turn violated, when do we consider it to be stealing? And the answer is that it sort of comes down to what we as a society think is right and jury is literally still out on that question. I've made some arguments with justifications for what I think the answer should be.
*now if an ad maliciously takes information from the user that might be a different issue. But I guess internet privacy is something that is really still being worked out. The same goes for advertising.