Plastic is responsible for litter and we should get rid of it because it is bad for the environment.
Whether the litter is paper, metal, glass, or plastic, the cause is human behavior and the solution is to change that behavior through education and regulation.
We should not get rid of plastics because, as you can read here, they are usually the greenest option. Plastics are better for the environment than other materials, so replacing them would do more harm to the environment. Plus, no more plastics would mean no cars, no internet, no cell phones or computers, no medical devices, no electricity or water to our homes, and so on.