More importantly, not everyone uses an ad-blocker (especially mobile users). If installing a browser extension becomes necessary to deem a browser worthy of use, I would think that's a problem.
When I was young no one really questioned ads in television shows, when I got to uni I kind of stopped watching anything but cable. Then netflix came out and I dropped cable alltogether. Every once in a while I find myself watching television at someone elses house and the constant ads completely destroy any enjoyment of the entertainment, even if I never really questioned it as a kid.
that's how the web is for people who don't run ad-block. They have no idea what it can be.