why do poeple think kids with cystic fibrosis are un-healthy?

i was looking up smoking weed and cystic fibrosis and poeple were like go ahead do it your lungs are already a mess and it pisses me off if you keep your lungs healthy your fine with cf (i have it) i wrestle play football o yah im 14 ive never been in the hosbittle for it im pretty big for someone whoi has it( for any one that dosent know many kids with CF are small and under wieght im 5,10 180 but why do poeple think that poeple who have cf are un helthy