"Just use a different service!" people will say. Great, until other services also terminate your account.
Yes these are private companies, but a very small number of them have tremendous control over what people see and hear online. The ideal of free speech overcomes the ideal of private corporate autonomy for me, and I believe it does for most.
The nature of social media and online services requires we rethink regulation. People should not be kicked off of platforms and services unless they are using those services to break the law.