A couple of companies have been burned by that when a large number of customers all filed for arbitration at the same time. Because the company is responsible for the arbitration costs, it quickly became much more expensive than defending a class action lawsuit would have been. Arbitration is good if you're only expecting random one-off lawsuits here and there but if you're going to anger a large number of people, using it as an alternative to the legal system can quickly backfire.

I should've put my emphasis on the "anything" part, surely there will always be aspects that can't override established law. At least for now, who knows if in the future Zuckerberg sneaks some Droit du seigneur [1] clause into Facebooks ToS once Silicon Valley has successfully "disrupted" Bodily integrity.

[1]: https://en.wikipedia.org/wiki/Droit_du_seigneur