These massive websites/broadcast SMS cannot have it both ways.
They cannot seek the protections of being "critical infrastructure" of any sort, common carrier, public forum, etc. and then, at the same time, disable user accounts for any reason just like any other private website.
They have to pick one or the other. The arguments I am seeing online are folks who have chosen one or the other and are arguing from their chosen perspective. For example, I am content to see them as just another handful of private websites, no matter how large they have become.
Meanwhile, the companies themselves, like Twitter, are content to bask in this ambiguity instead of clarifying what they are or intend to be.
EDIT:
Once the number of users has grown past a manageable threshhold where violations of rules can be detected by administrators (instead of relying on others to report them), it may cause some to wonder what are the reasons absent any legal or other compusion when a user's account is suspended.
Looking at the Twitter rules, the possible reasons this account may have been suspended, e.g., copyright violations, are not obvious. What is their justifcation for suspension. Some sources, e.g., The Verge, are reporting that this Twitter account was being used to solicit statements of support from academics to be used in some litigation in India that seeks to block access Sci-Hub in that country. Apparently the Indian court denied the initial request from publishers for an immediate decision in order to allow time for the scientific community to weigh in on the issue.
I hope someone is setting up another means for the scientific community to weigh in on the non-monetary value of Sci-Hub.