The problem with ads isn't that they're present on screen (though that can get annoying), it's that their presence causes a fundamental misalignment of incentiv

The problem with ads isn't that they're present on screen (though that can get annoying), it's that their presence causes a fundamental misalignment of incentives. A paid service without ads is primarily incentivized to provide value to the customer. An entirely ad supported service is incentivized to provide value to advertisers first, potentially to the detriment of the users, and to users only to the extent that it brings in more ad money.