While it seems rather obvious that inhaling carcinogenic fumes is bad for your health, I’ve never really found a study that shows harm by second hand smoke as serious as the harm of smoking itself, to be honest. I don’t think the damage second hand smoking does to the general population’s health is quite as bad as direct smoking is.
Second hand smoking is bad, but it’s orders of magnitude less dangerous than sucking the carcinogens straight out of a burning cigarette according to the papers I’ve scanned through. It’ll increase the healthcare cost a few percent, but it’s not as significant across the entire population as you’d think looking at the individual risks.
If we can end smoking, we’ll end secondhand smoking for free. Plus, places and people just smell nicer in general.