Most free web sites pay for their upkeep with ads. It has been an unwritten agreement since forever (or at least as long as there have been ads on the web) that if you consume the content, you pay the creator by looking at the ads on their site.
Consuming the content without looking at the ads is like shoplifting because you don’t like the way a store’s checkout counter works and/or the fact that they want money from you at all.
Remember print magazines and newspapers? Ads pay a large portion of the costs of producing them, but no reader is obliged to look at any ads at all. Advertisers pay for a chance to be seen, not for an obligation for anyone to look at them. Since nobody has any obligation to read the ads, avoiding them cannot be a violation. You pays your money and you takes your chances.
I was working with a different definition of ‘look at’. When reading a magazine (according to my definition), you will look at the ad, because you never know whether a given page will contain an ad or editorial content. Your eyes will fall upon the ad, and then you move on, likely not really taking it in unless it manages to catch your eye. Same with me and web ads. Most will barely register, as the majority is really not that interesting - but sometimes, I will take a closer look, and very occasionally even click on one.
