You're right - I don't get out much or live in a crowded city. I live in a small town (pop. 3200) town in Texas and you can drive for miles around it and see a lot of open space. You can also see tons of trash alongside the road that pigs have thrown out of their cars. All that litter wouldn't be there if we didn't have so damned many people on this earth. And Texas is not the only state with litter bugs.
Based on litterbugs, you have decided that mass execution of humans to reduce their numbers is appropriate? Have you considered a more constructive approach like getting community groups to adopt stretches of the roadway to perform periodic cleanup? That beats the hell out of littering the planet with rotting bodies in addition to the trash. You could even make a business out of recycling that litter along the roadways.