It will never become cheap enough to do a 51% attack because there are multiple parties that all would be interested in doing a 51% attack competing against eac

It will never become cheap enough to do a 51% attack because there are multiple parties that all would be interested in doing a 51% attack competing against each other. Furthermore, Bitcoin is "self-healing" in the sense that an attacker does not gain persistent control; they lose control if they lose 51% compute vs the rest of the planet (unlike, say, Ethereum with proof of stake).