It's also important to remember the differences between many of the Bonus Marchers and the Regulars led by MacArthur. If memory serves, most of the Bonus Marchers were United States troops...short-term volunteers who had been promised bonus money (not unlike the mechanism used to enlist Volunteers at the state level during the Civil War). The Regulars, especially the officers, were longer service types who viewed themselves as professionals. It would have been easy for MacArthur to view them as something less than veteran soldiers. There was also a longstanding fear within the Army proper (especially within the professional officer corps) of social anarchy (reading back through articles written for The Army and Navy Journal as well as the handful of professional journals in the 1880s through 1900 or so is an interesting experience...much concern about urban unrest and anarchists).

As for MacArthur...he took after his father when it came to disdain for civilian leadership.