They become compliant/complicit hostages when they stay and pay.
that is a very good point. WHY did n’t they get thrown out by the management?
Actually, even paying customers do not have the right to disturb other patrons of the establishment with their speech or behavior. It is commercial private property. And definitely not a public protest, 1st Amendment free speech zone.
However, I understand management may have been caught flat footed this time. I would pay my bill but I would make it very clear when I did that, unless management acted to restore decorum going forward, they would have no further business from me and that I would ensure that all my friends knew about the inhospitable dining environment as well.
As for management, assuming they have the stomach for it, a decision to confront the protestors with a lawyer-prepared demand that they cease their disruptive behavior and depart the premises or face the police on a disturbing the peace complaint call might convince them to go back outside onto the sidewalk where they can protest their little hearts out while being ignored by the rest of society.