Cat and mouse forces new less efficient spam to be created
Existing transactions may be frozen indefinitely
Centralizes moral control to a small subset of individuals
Increases regulatory risk for developers and node operators. Morality rules open the door for requiring code changes to accommodate KYC, AML, and SDN lists
Creates challenges for wallet developers to keep up and change what can be allowed and what can't. Particularly for multistage TX to decay required signatories on multiple transactions for businesses, trusts, wills
It would fully capture bitcoin as we know it and it's value and utility would be constrained