You can kind of have both but it's an outright hard problem.
If you have a functional governance system, you can implement some form of vetocratic de-listing mechanism. It doesn't have to stop the de-listed item from trading but it is a mechanism for a community to collectively decide what is and what isn't a scam/forgery/theft/etc. This same system generalises to a central source of trust for a given network, service, or protocol where the control is decentralised.
Now this falls back to the first condition which is to have a functional governance system. Any failure in the governance system is now a failure in your system for deriving trust.
Can it be done? Yes. Has it been done properly yet or even really been done at all? No not really.
This isn't to say that it's impossible but we aren't there yet by any stretch of the imagination.
For that problem it could work, but it would never work for the problem that exchanges face where people get their credit cards stolen, or a government seizes some user's BTC, etc.. and the exchange gets hit with big chargebacks and other fees.
If you have a functional governance system, you can implement some form of vetocratic de-listing mechanism. It doesn't have to stop the de-listed item from trading but it is a mechanism for a community to collectively decide what is and what isn't a scam/forgery/theft/etc. This same system generalises to a central source of trust for a given network, service, or protocol where the control is decentralised.
Now this falls back to the first condition which is to have a functional governance system. Any failure in the governance system is now a failure in your system for deriving trust.
Can it be done? Yes. Has it been done properly yet or even really been done at all? No not really.
This isn't to say that it's impossible but we aren't there yet by any stretch of the imagination.