largely harmless at the levels in cigarettes and vapes for the primary smoker
The cardiovascular effects of nicotine over the long term are likely not harmless at all. There's no reason to believe that combustion is the reason PAD, stroke, and other cardiovascular disease is associated with smoking. There is a very good reason to believe that a potent vasoconstrictor is, however.
That's the fucking point of the trolley problem. How can so many people get here and not fucking understand it's supposed to present the dichotomy between utilitarianism and deontology. If you have a duty to not commit murder, and pulling a lever murders people, you can't pull the lever. It's a valid position.
If deontology is wrong, we should immediately round up every depressed person, kill them, and harvest their organs.