If someone gives you an ad filled magazine, you can rip out the ad pages and throw them in the trash, leaving only the articles you actually want to read. Same principle applies here. If some random person on the street gives you a propaganda pamphlet, are you obligated to read it just because some businessman paid for it? Of course not.

Edit: let's step through this. If I use a towel placed over the computer to block ads, that's morally the same as using blocking software, I think? If I block the ads by putting my fingers in my ears and staring at the ceiling, also the same thing, morally. If I block them by watching them in a negative frame of mind, saying that I dislike ads and won't do what they suggest, I'm still doing the bad thing, the same as using an ad blocker - if it is a bad thing. My obligation, if it is an obligation, is to be receptive. Otherwise what, it's a sort of mind-fraud?