Smoking, the government telling people when and where they can smoke tobacco.. That's when it all began...
Yes. I often point to the tobacco topic. I don’t think it’s about the smoking (plenty of people really hate smoking) but it’s about the control. Without making something illegal, the government learned that it could control people and private businesses pretty much on a whim. The non-smoking section came first. Then the smokers were relegated to a designated smoking section. Then smoking was banned from inside entirely. Then smoking was banned around the exterior door. Bit by bit the control is extended. It’s been all downhill since then.
I'm going to go with seatbelts and/or motorcycle helmets.
If smoking impacts another's health, then that's enough to open the door for the government to act.