It shouldn't be necessary to mandate a specific style but if you only ban brutalist architecture (pretty clearly the point of this EO) they'll just call it something else. The real problem though is having people in government who agree with the purpose of brutalist architecture in the first place. (Something Trump will never address because he's owned by the same people) It isn't just ugly depressing slop due to bad taste, brutalist architecture is meant to intimidate, alienate and demotivate the viewer. It's the architecture of communism, which is why brutalist "architects" care so much about getting federal building contracts in the first place. Building their eyesores on private property would defeat the point because private business can't compel people onto the premises. TL:DR: forcing people to look at brutalist architecture should be considered a human rights violation.