Another idea would be legislature. Have these online public spaces serve under the same laws as real-life public spaces (museums, parks et cetera).
If a town banned you from the train station because you refuse to give them your phone number, that would open them up to being sued. That should absolutely apply to Discord, Google Mail and Amazon AWS.
If a town banned you from the train station because you refuse to give them your phone number, that would open them up to being sued. That should absolutely apply to Discord, Google Mail and Amazon AWS.