I don't consider it theft one bit. Just like I choose which websites to visit, I choose which content I see on my screen. On sites I regularly visit like v7n, wtf, etc ad blocking is turned off.
I really only started ad blocking for 2 reasons:
1) News sites that throw big animated adverts right in the middle of a story. It's annoying and distracting. I don't know why people click on them, it on encourages the fools more.
2) MFA sites. I don't want to see 3 adsense blocks, stacked on top of each other before I see the content. Thank you very much. :p
I also block all flash using
Flash Block, that takes care of those stupid sweep in advertisement overlays.