Not a utility, but they are a provider of computer services and presumed to be a public forum which grants them immunity under the Communications Decency Act from lawsuits related to what their users might do on their platform. If they act in a biased way while moderating the site (which we all know they do), then they are not a public forum and lose that immunity.
Cruz hits the nail on the head here... Now the question is will they do anything about it?
