I agree with you that most internet content and mobile apps could not exist without advertising because they would not be profitable.
But similar to D&D alignments, whether something is profitable is completely orthogonal to whether it is ethical. Human endeavors may be profitable but not ethical, ethical but not profitable, both profitable and ethical, or neither ethical nor profitable.
So I share the parent commenter's concern about people who seem to be claiming that a thing must be ethical because it is necessary to be profitable. It's perfectly possible for a profitable thing to be profitable-good, profitable-neutral, or profitable-evil.
I agree with this separation of concerns, but you have to paint the full picture.
Without ads, we have a pure ethical situation. Desirable content and an eager reader to consume it. All is good. Except for the fact that this content cannot exist unless the producer runs ads, which some consider unethical.
If we end the story here, the content disappears since there's no ethical way to sustain it. So the original ethical transaction (content -> reader) is gone. Also known as throwing away the baby with the bath water.
If we are to complete the picture though, you might as well claim it's the consumer being unethical here, for flat out refusing to offer any payment for a service they want, and clearly costs money to produce.
Perhaps you are right. I can think of a couple additional considerations:
First, it's worth acknowledging that some amount of desirable content already exists without advertising. My partner and I pay a subscription to three streaming services, a couple local newspapers, a town newsletter, and a physical news magazine. Besides the magazine they do not use ads to supplement their revenue. Having said that, I certainly agree that content that is only marginally valuable to people (who have money) would cease to be profitable and would therefore decrease in a world without advertising.
Second, I think it depends on to what degree you believe that the ends can justify the means. How acceptable is it to manipulate consumers if it means you can achieve a more ethical end like giving them desirable content? Do those things cancel out? Personally I think it depends on how unethical one finds the advertising and how beneficial one finds the content. We already restrict certain kinds of advertising to children or for addictive substances. Many countries do not allow advertisements that encourage consumers to request brand-name medications from their doctors, and China has even banned advertisements for luxury products. Many people are concerned about advertising that creates unrealistic body expectations in children or promotes excessive levels of consumption.
(Having worked on a DARPA project in a war zone a decade ago, I have spent a lot of time thinking about to what degree the ends justify the means, and I still have no good answers.)
But similar to D&D alignments, whether something is profitable is completely orthogonal to whether it is ethical. Human endeavors may be profitable but not ethical, ethical but not profitable, both profitable and ethical, or neither ethical nor profitable.
So I share the parent commenter's concern about people who seem to be claiming that a thing must be ethical because it is necessary to be profitable. It's perfectly possible for a profitable thing to be profitable-good, profitable-neutral, or profitable-evil.