How did we get here:

By way of explanation, the Supremes long ago extended individual rights to corporations. Attempts to limit those rights have been rejected as unconstitutional--as now seems likely in their right to spend in elections. Is their right to vote next?

They already have the right to vote!! They just don't have to go to the voting booth like us common people. Many of our elected representatives are simple automatons implementing the commands of their corporate sponsors. To bad that I (as an individual) have to go through making my wishes known through the voting booth and then I don't even know which way they will really vote in any event. It would be much simpler to take the vending machine approach. I put a few $$ in the slot and the Congress person votes my way. Simple.

The classic dystopia is subjugation by robots or aliens.

We are so busy worrying about intelligent machines or alien impostors taking over control of civilisation that we've failed to notice a certain other class of immortal, quasi intelligent being installing itself in vital positions of power.

What traitor to mankind took a backhander to grant corporations personhood?

And is it too late to undo that calumny?

It's not too much of a leap to equate incitement to terminate all corporations' monopolies as a threat against their lives (qua economic viability). Thus, to make public statements against monopoly is to incite violence against corporations. And to suggest they're not persons is akin to the suggestion that a class of humans are animals.

The trouble is, as in the movie 'Invasion of the Body Snatchers', the corporations are already in power, and the 'Something must be done!' insurgents are simply being ignored by an ever dwindling population of people who might care.

There are at least two other classic dystopias. In one, we blow ourselves up and wind up back to medieval-style feudalism, if not the Stone Age. In the other, favored among cyberpunk authors especially, the corporations take over.

The question is though, Zerbulous, are corporations fully sentient? I suspect their cognition operates at a slightly slower speed to that of the human, and is intelligent only in the same way that a predatory dinosaur may have been intelligent. Colossal, inexorably superior in every respect but creativity and dexterity.

Recognising corporations' right to bear arms as a means to rectify a government that failed to act in their interests (failed to properly husband parasitic organic entities), is not what we should suppose the founders had in mind.

Who can yet say "Hang on a mo. Corporations are golems of the legislature. They aren't human and shouldn't be treated as such!" and have a hope of catalysing a remedy?

Corporations are now so numerous and so powerful, that they'd vaporise anyone who got near their off button (if they still have one).