For the record, I don't have a problem with people smoking in their cars (if there are no children in said cars). I do have a problem with people littering. Cigarette butts are litter. Smoldering cancer sticks thrown out of windows can ignite other fuel and cause a fire.
I don't know why people think it's OK to litter with cigarette butts. It seems that even smokers would admonish my behavior if I threw my empty glass bottle by the side of the road. Or an empty energy gel package. Or what about a giant bag of fast-food packaging leftover after consuming greasy goodness? Or if I got a flat on my bike and left the old tube with the hole in it alongside the road. All of it is litter.
I'm not perfect. I have on occasion thrown stuff out of my car window. Sometimes it almost seems like you just about have to do it. However, I pick up way more than I throw down. If everyone had the same ratio of trash picked up to trash disposed as I did, the streets would be as clean as they are in Sweden.