Plastic bags in trees and alongside roadways, garbage on front yards and litter in the streets are all caused by human misbehavior, not the object itself. Going back a few years, here are two photos showing the Washington Mall after, respectively a pro-Obama rally and one held by the Tea Party. It's a fair bet that both groups brought the same amount of paper products to their events.
In fact, you can search Google Images, combining "trash", or litter" and any anti-anything protest conducted by our left: from Occupy Wall Street to Keystone Pipeline to most recently, the anti-ICE encampment in Portland and find similar photographs, along with reports of taxpayer-paid employees forced to wear Haz-Mat suits to remove human waste.
The Left, expects everything to be free, and paid for by someone else, so it's really no surprise that they dump their garbage where it falls. They probably don't make their own beds, though at least our Greenwich greens have maids to ensure that they'll have clean sheets to tuck into each night.