If 51% of the mining hashrate get together and say they'll include only OFAC-compliant transactions, and they'll build only on top of OFAC-compliant blocks, then we'll have a cartel of miners that cannot be beaten. They'll agree to exclude miners that don't sign up to their rules, and those rules will change in arbitrary ways to suit the leaders of that cartel
Miners outside that system will earn nothing, and will quickly stop mining
It's critically important that the relay network continue to be designed to help small miners and new miners, that is the real subtext of the Core versus Knots argument.
