That doesn’t answer my question. The question isn’t what ways there are to generate revenue, it’s what is the right metric. Number of users dropping doesn’t mean that revenue is dropping, so it’s not a great metric to demonstrate that ads are bad. If we want to show that adding ads to a site is damaging, we have to show that it’s actually damaging, rather than you lose a fraction of the people who were mooching anyway.
I’m not sure I agree there are lots of ways to generate revenue, and more importantly that there are reliable ways to generate revenue when bootstrapping a small company. If there were reliable ways to do it, ads wouldn’t be such a big problem. The scourge of ads is evidence that finding revenue sources isn’t reliable.
The main sources of funding for small companies are: loans, grants, personal savings, friends & family, angels, VCs, sales, and ads. Sales and ads are the only sustainable long term strategies unless you’re going for government funding of research or a public service. Sales requires a product with market fit, i.e., a bootstrapped company. For most early stage companies that leaves only ads as a potential positive long-term revenue stream. What other options are there?
Making money with ads requires an audience, which requires having something of value. In that sense, it does require development effort. Maybe installing the ad into an iframe is easy, but getting enough people to your site isn’t trivial.