Their entire business model of distributing arbitrary uploads is a grant from the government, one which was very controversial until the overton window passed.
edit: We can certainly decide that it's in the public interest to place limits on the editorial control over sites that rely on safe harbor, just as phone companies aren't allowed to censor particular conversations. Things get to be rights because we collectively decide that they are.
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edit: Deleted, because it is completely wrong.
[Your libertarianism ignores the law. In order to qualify for safe harbor under DMCA, their ability to exercise arbitrary editorial control is limited. If they want to choose what they host, they are choosing to be legally responsible for what they host.]
That's not actually libertarianism; it's crypto-fascism. There is no distinction between a totalitarian government and a perfectly "libertarian" company which owns all land and property, so true libertarians must be concerned with how power is actually distributed.
Tech giants have scale and effects on par with government, especially as these "independent" companies tend to make decisions in lock step. Thus libertarians should be primarily concerned with the rights of the distributed actors within these ecosystems.
edit: We can certainly decide that it's in the public interest to place limits on the editorial control over sites that rely on safe harbor, just as phone companies aren't allowed to censor particular conversations. Things get to be rights because we collectively decide that they are.
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edit: Deleted, because it is completely wrong.
[Your libertarianism ignores the law. In order to qualify for safe harbor under DMCA, their ability to exercise arbitrary editorial control is limited. If they want to choose what they host, they are choosing to be legally responsible for what they host.]