A publisher has the right to regulate the content they publish.
A common carrier must strictly avoid regulating the content of their carriage.
There are different regulations in place for different businesses. A common carrier must scrupulously avoid even the appearance of modifying or restricting the information they carry.
The grey areas lurk in what publishers condone and promote: what constitutes hate speech or child pornography and is subject to reasonable restrictions on speech in a free and democratic society at one end of the spectrum, and what constitutes political campaigning and is subject to campaign finance and political contribution laws at another.
Does "common carrier" describe any social media website? All social media sites, besides choosing what content to allow, make many decisions about what to promote. (These decisions are usually made algorithmically, but not exclusively, and the choice of what algorithms to use and how to tune them is still very opinionated.) The common carrier rules seem intended for companies like phone providers and ISPs that don't make any decisions about what people should use on the platform. In comparison, social media sites seem like more open versions of newspapers and TV stations.
I think it's clear that organizations that publish content to the web are publishers. They just don't want to be saddled with the responsibility of more traditional publishers and all that that entails. They're "disruptors" for gosh sake, not media presenting content to consumers as a means to generate revenue.
A common carrier must strictly avoid regulating the content of their carriage.
There are different regulations in place for different businesses. A common carrier must scrupulously avoid even the appearance of modifying or restricting the information they carry.
The grey areas lurk in what publishers condone and promote: what constitutes hate speech or child pornography and is subject to reasonable restrictions on speech in a free and democratic society at one end of the spectrum, and what constitutes political campaigning and is subject to campaign finance and political contribution laws at another.