The difference is that stores and malls invite the public in for a limited non-protected purpose - shopping or other commercial activity. Twitter invites the p

The difference is that stores and malls invite the public in for a limited non-protected purpose - shopping or other commercial activity. Twitter invites the public in to exercise free speech, which in a public space would be protected. This invites an analysis that Twitter may be a quasi-public space that offers some 1st Amd. protections.