Only that a company can't have a policy "no blacks, no women, no Jews, no old people". They can have a policy that says "any swearing you're out", "any incitement to violence you're out", "any spreading of demonstrably incorrect information and you're out". The obvious response to the last one (your bolded part) is "who decides". And the answer is very simple: "they do", they own the platform, they 100% have the right to decide what they want the community to be like. Its entirely likely the powers that be at Twitter had a long think and asked themselves "do we want to go down in history as the prime enabler of this person". The 1st amendment applies solely to the US Government, "freedom" also applies to people and companies to decide how to run their platforms.