You make it seem like you disagree with the person you’re replying to. But don’t you see? You agree with him. That exactly what he’s saying: what Twitter legally can do is different than what they should do.
Even if Twitter wanted to promote freedom of expression, there's an inherent contradiction between allowing others to express their opinion and them expressing their own opinion. I think someone whose promotion of freedom of expression involves denying themselves that same freedom is sending a mixed message. Because their support of the principle would have those reservations, they don't have an obligation to provide it.
Twitter has claimed in their own promotional material to support free expression, so it may be a bit disingenuous for you to suggest they may not want to promote free expression.