Who, other than you, says that twitter must be just? The world would be a completely different place if companies were required by law to be just.
For example, when it comes to publicly-available services such as this, we often hear about people referring to "Twitter's freedom of speech" in terms of censorship of its users, which boggles my mind. Twitter provides a publicly-accessible service that allows users to post short entries, and when they prevent someone else from posting something, it basically amounts to "Twitter's right to free speech is more important than the user's ability to speak" and that seems a bit counter-intuitive.
If Twitter's policies are unjust, then Twitter does not deserve the level of influence that it has. My opinion is that such a service could not have been foreseen by the writers of the Constitution. In their day, the greatest threat to freedom of speech was the government. Remember, they had just fought for their independence from England. I don't think they could have envisioned a world where the greatest threat to free speech would come from the private sector.
And if we're not careful, we're about to be making it worse. As it stands, platform operators are not generally liable for the things they automatically publish on behalf of their users, outside of certain highly egregious things (such as child abuse imagery), and even then only if they don't follow the proper procedure with regards to reporting to law enforcement, etc. If that ever changes, expect freedom of speech to be null and void in context of the Internet.
Why do you assume that it is integral to modern open communication? (hint: it's not, for plain reason that twitter does what's best for twitter)