The argument against ads (and thus, for ad-blockers) goes like this: Bob (the person providing/selling ad-space) is selling Alice (the advertiser) something (the reader's attention) that doesn't belong to Bob in the first place. It belongs to the reader, and the reader has chosen to pay attention to the article/whatever, not the ads.

That said, I like AdBlock Plus, and here's why: by default, it doesn't block 'acceptable' ads; i.e. if everyone used it, only the Website operators who show very nice/unobtrusive advertisements get through, and therefore get paid.

https://adblockplus.org/en/acceptable-ads