For years, people have longed for ways to stop advertising from popping up on their iPhones and iPads. Now, software to block ads on these gadgets has arrived — and the harsh realities of the practice are causing second thoughts.

Just two days after Apple enabled ad-blocking apps through its new mobile operating system, iOS 9, users are embracing the new technology after long complaining that the ads track them, slow down web browsers and are just plain annoying. In less than 48 hours, several ad-blocking apps with names like Peace, Purify and Crystal soared to the top of Apple’s App Store chart.

Yet some web publishers are now fretting that ads on their sites can’t be viewed because of the blockers, which could threaten these publishers’ livelihoods. On Friday, the maker of the $3 ad-blocking app Peace, Marco Arment, removed his program from the App Store and offered refunds, saying that while stopping ads does “benefit a ton of people in major ways, they also hurt some, including many who don’t deserve to be hit.”

This about-face highlights the complexities around the ethics of ad blocking. Advertising underlies much of the Internet, making it possible for people to make a living off the Internet and create the content that users consume. By limiting ads, that implicit contract was violated, some publishers and advertisers said. More distinctions now need to be made around what qualifies as “good” online advertising versus “bad” ads that should be blocked, they said — though they were less clear on who would decide what constitutes a good or bad ad.