Those are the exceptions, not the rule. But also, you're wrong: most polyps would not become cancerous -- only 5%-10% ever do. As a preventative intervention on otherwise healthy people, colonoscopy is one of
the most effective things we do, and it's not that effective [1].
You've also included vaccines (which I explicitly mentioned) and "taxes" (which are not medical interventions), so you've completely missed the point.
[1] The NordICC trial found an impact of 0.03% on risk of death from colorectal cancer, which was insignificant. It did find an 18% risk reduction for getting colorectal cancer, but this didn't translate into a survival benefit.
https://www.nejm.org/doi/full/10.1056/NEJMoa2208375