No government organization/bureaucracy should be allowed to do their own hiring.
To allow them to do is is to allow them to build their own ideologically homogeneous power base. If the hiring is diverse (meaning ideologically, educationally, experientially, and demographically - not skin color or ethnicity), it will eventually weed out the scum.
Who, then, is to do the hiring and firing ("weed[ing] out the scum")?