Twitter has the freedom to allow public officials to use the service for either personal or professional purposes. Many government agencies in many countries use Twitter to communicate with citizens via the service, similar to how they use Facebook or e-mail.
As far as President Trump goes, Twitter has had to make policy exceptions in order to ensure his continued access to the service, AND legal proceedings have also resulted in rulings that govern his specific use of the service (for example, he's technically not allowed to block citizens.) As such it's not especially useful to look at Trump's experience on Twitter and try to generalize it to anyone else.
I am not saying they shouldn't ban accounts or allow free speechers. But I don't buy they should be allowed to do whatever they want because they are private company. If the past hack resulted in market manipulation or a bigger shit show, should twitter be liable for that?
As far as President Trump goes, Twitter has had to make policy exceptions in order to ensure his continued access to the service, AND legal proceedings have also resulted in rulings that govern his specific use of the service (for example, he's technically not allowed to block citizens.) As such it's not especially useful to look at Trump's experience on Twitter and try to generalize it to anyone else.