Well then what constitutes misinformation? Is speculation misinformation? Are opinions misinformation? How does misinformation differ from someone exercising their right to free speech, but miswording what they say?

I think that is a slippery slope. In fact you just described communist russia where the government would get citizens to turn each other in for saying the wrong thing(this can easily be used for nefarious purposes). You are now allowing the government to suppress less-popular opinions by labeling them misinformation.