After rereading a few times, I think I've parsed your argument:

That X enables many businesses to exist doesn't mean that X is a good thing on balance, because X itself can have harmful effects that outweigh the benefits.

This is of course true, and I can look past the inelegant phrasing.

But to make this a credible argument you need to argue for why the costs of advertising outweigh the benefits.

> What’s hard for you to understand?

They're looking for depth where there isn't any. You're attempting to prove advertising is bad by claiming it's like lead pipes, on the basis of them both being bad. It's tautology. One could similarly "prove" ad blockers or puppies by this analogy to be whatever because they, too, can be good or bad.

Please read again.

Modern advertising is what I'm against, not advertising as a whole.

Similarly, I'm against lead pipes for plumbing, not plumbing as a whole.