Cindie, that has been blown 'way out of proportion, a unit that size is only sufficient to do something like regain control of one single local disaster at a time, like New Orleans during Katrina (And actually would be very stretched to do even that, if as in NOLA the civilian law enforcement agencies have gone catatonic), and that's all that particular mission is really intended to address. Even plussed up with all its service support attachments, a BCT is only around 5,000 guys, which is a fraction of the total law enforcement personnel establishment of any large metro area.
It's a favorite blogger bogeyman, but the actual mission for which forces are designated is a valid one.