"I would not want to contribute to more chances for a friend to get cancer"
Once again, if you have capacity, then you have the right to decide for yourself what you do. No-one has the right to take that control away from you, unless you are into child porn etc and go to prison, of course.
Where do we draw the line? I don't agree with fizzy drinks, i would rather than my friends don't drink them, or eat meat etc.
My DD goes horse riding, her friends go Kayaking, which thanks to another thread i have just found can be a health hazard.
I cannot believe that posters think they have the right to impose their opinions onto others to this extent, it is oppressive behavior.
This is a ethical issue which is debated by those delivering care to the disabled, which i have had to think about, in the course of my work.