[Edit: Following the incentives of the protocol is not collusion. In a crypto context I would define collusion as something like multiple parties working together against their own incentives (e.g. rejecting valid, fee-paying transactions).]

If a majority of banks and businesses agree to block transactions of a known terrorist, is it collusion or cooperation? I don't see a meaningful distinction at that point, other than the negative connotation of "collusion" poisoning the well. Which is why I referred to "cooperation" instead.

Humans are social creatures and collusion is the natural order. Humans will cooperate unless doing so is clearly to their detriment.

if they can pursue their own interests freely and if those interests they pursue align with the majority or the totality it does not negate their decentralized nature.