Over the years adverts have become not just an annoyance, but a significant security risk. Google & co. have an appalling record when it comes to vetting adverts - if indeed they do so at all.
Search Google for something like Adobe Flash Player or Adobe Reader and top of the page will be sponsored links (adverts) to scam websites.
And there can be highly targeted attacks on entirely legitimate websites.
For example, the official web site for Exact Audio Copy shows adverts served up by Google (or similar) on most pages. There are only one or two modestly sized banners, which are hardly intrusive or obstructive, and they earn the author of a very useful piece of freeware a small income to help cover his hosting costs.
But a few years ago someone created a banner advert, which simply said something along the lines of ‘Click here to download Exact Audio Copy’, used Google’s advertising system to have it placed on the EAC download page and redirect many casual users to their own highly questionable software site.
I feel sorry for the thousands of excellent sites who are denied their only source of income by ad blockers. And for well-behaved sites I visit repeatedly (such as this one) add an exception to automatically disable the ad blocker. But the web mass-advertising system is been fundamentally broken, one could even argue it was designed to be so, and urgently needs fixing.