I used to ask the same questions, but then I've realized: this line of argument tries to justify non-action on known known because there are also known unknowns

I used to ask the same questions, but then I've realized: this line of argument tries to justify non-action on known known because there are also known unknowns and maybe even unknown unknowns. Now what? Smoke a cigarette because we know that unknown carcinogens exist that are not included in cigarette smoke?