>a reduction in smoking might decrease cancer

I understand that you were trying to make a different point so forgive me for derailing this conversation but this is important and I want to be emphatic.

Smoking incontrovertibly and substantially increases your risk of developing cancer. 85-90% of lung cancer cases and a substantial number of other forms cancers of can be attributed to smoking. There are a lot of ways to study this (you can look at people that never started smoking, not just people who quit). Yes, these studies are correlational (we don’t do RTCs on things that can kill you) but they are very high powered and are designed to account for confounding variables. The entire reason we’ve seen a decline in cancer mortality in the US since the 90s is largely attributable to falling smoking rates beginning in the 70s. And while much fewer people smoke, roughly 1 in 7 still do. Encouraging them to find another way to feed their nicotine addiction, and discouraging young people from ever picking up the habit, would save a lot of lives still.