Because they've never smoked before and if they have and are still against it they probably had some bad **** tbh
I was against it for a long time because of the way people treat it. A lot of people where I'm from will post pictures or videos of smoking everyday or make posts about it on a daily basis and its so dumb the way they practically worship it. I think its something that if done should be done privately.
Its all about the information out there, and a lot of that information is incorrect or misleading. Oh well, it will be legal everywhere in the next 20 years.