As for the contract point, I think there is an implicit contract between the publisher and the reader that they can access the content for free as long as they are willing to accept the slight intrusion of the ads.
As for the ethical matter, I do think that he is being a free loader, accessing content which is free only because of the many who do not use an ad blocker. In one way therefore he is cheating and that is unethical. It is perfectly fine, selfish and normal behaviour, but hardly angelic or ethical simply because he is not fulfilling his part of the bargain.
If he hates adverts so much and a significant minority acts as he does then publishers will either be forced to start charging for their content as Times Online has began to do and as they do for books, or valuable information will stop being generated, thus, making us all poorer.
Finally, this is capitalism, if you do not like it, you might be welcomed in North Korea or at least in China.