Could a Platform's Terms of Service Defeat Legislatively Imposed Common Carrier Obligations?
Some commenters on the Social Media as Common Carriers thread suggested that social media platforms' Terms of Service, which users must sign, can defeat any common carrier obligations that are imposed on them.
If the argument is a normative argument—property owners should have the right to limit their visitors' use of the property, including by contract, and that common carrier status for them is improper—then I see its appeal, though I'm not sure that it ultimately carries the day.
But if the argument is that the Terms of Service would constitute a waiver of the platforms' nondiscrimination obligations, even if such obligations are imposed by a common-carrier-type statute, then I don't think it will fly.
The closest analogy I can see is the traditional common carrier duty to "exercise … care and diligence" towards their customers and their property, which the Court has held could not be waived: "[I]f a carrier stipulate not to be bound to the exercise of care and diligence, but to be at liberty to indulge in the contrary, he seeks to put off the essential duties of his employment." N.Y. Cent. R. Co. v. Lockwood (1873).
Likewise, if a nondiscrimination duty is imposed on a social media platform (analogous to such a duty imposed on traditional common carriers), the platform likewise can't stipulate not to be bound by that duty. And of course there's no reason to think that Rumsfeld would have come out differently if a university required all recruiters to sign agreements that they will recruit only if their employers forswear sexual orientation discrimination. See also Alexander v. Gardner-Denver Co. (1974) (holding that employers can't require employees to preemptively waive their rights under nondiscrimination statutes as a condition of employment).