Solipsism is a pretty solid argument. It just doesn't mesh well with free will. We're all just dissolving chemicals perceiving the world through a single uniform experience. We just can't communicate we're the same because no matter what medium we try to communicate the message with, we affect part of the chemical now. No matter what, the message deviates into the environment and either vibrates into a disagreement or vibrates into a perfect hive mind. (Disagree with me, I dare you)