Yes. They are not legally required to provide service to anyone.
But indiscriminately providing services to everyone (within the laws of your country),
without booting people based on a personal agenda, is the ABC of gaining the trust of your users.
But people aren't leaving twitter because they perceive it as favoring one side. People are leaving because they are being flooded with hateful, abusive comments from trolls and their bots. So it seems the key to gaining trust is creating a place where users don't experience rampant abuse.
It depends on what you mean by 'personal agenda'. If someone is directing hate speech at other users, would it be pursuing a personal agenda to ban or otherwise sanction that user?
It's not always easy to draw a line on conduct, but I think there is plenty of behavior on Twitter that 99% of people could easily identify as toxic.
Twitter and it’s not even close. A journalists synthesis of what he thinks the evidence is carries no weight. Twitter is like a mini trial. You hear the testimony from the horse’s mouth, people cite documentary evidence, and you weigh credibility to reach a conclusion.