Real life contracts sometimes turn out to have non-enforceable clauses within our legal framework, or may be entirely invalid if, for example, signed under pressure or false pretense.
Imagine if Goldman Sachs did this. A judge can say "look, you can follow our rules or we start seizing assets etc".
And when you're sitting around trying to be anonymous, well... you're doing everything on a public ledger, so now you're extremely restricted.
Hell, courts/legislative bodies could even go down the "force all miners within their jurisdiction to rollback an unwanted transaction". You think miners care enough to make a stand on this kind of stuff?
Unless you're going to like.... download your consciousness onto the blockchain you are still just as liable to being told by a court what to do as anything else.
US financial laws have been very useful for the gov't to be able to de facto give it worldwide jurisdiction in some areas, I think there would be relatively few qualms about continuing down this path. Especially if (for example) Robinhood and Coinbase were forced to follow along. At one point the "blessed" thing will become the only place you can really operate.
This would destroy the real-world value of this block, basically making it a digital equivalent of dirty money.