Know that you're the driver of your own car. No one else is in that car with you.
If it gets strewn with garbage and stinks, you have put it in there yourself or allowed others to throw their garbage in your car. And you've allowed it to stay there and rot.

Cleaning your own car does no harm to anyone else, except those that are used to throwing their garbage in your car. Roll your windows up. Do not allow their garbage in. Their garbage is their garbage, it has nothing to do with you.

Roll your windows down to others who aren't throwing their garbage in. Let them get a whiff of what a nice clean car smells like.
Now you can become an example to others, such as your children, co-workers, family etc.

And the greatest gift of all is you will enjoy your own car.