People have a right to use ad-blockers. It's their computer after all.

However, a lot of things that people like to use, and might even have been willing to watch ads in order to use, will not be viable if everyone used adblockers.

It's really that simple. However, most people don't like to acknowledge that given the opportunity, the will freeload of others, or that in some contexts freeloading is natural and not immoral