Technically it could be considered treason. One of the few actual legal definitions of treason include 'making war upon your own country', or conspiring to overthrow said government. It's a stretch, but taking up arms (I would not be surprised if every superhero in the MU was considered a potential WMD) against the lawful representatives of the government could be spun into a charge of treason because the logical move once you go past Iron Man is to go after the people that gave Iron Man his orders: the US government.
I suppose it would just be too 'political' for the heroes of the MU to be filled with rage and hatred not at Tony Stark but at the POTUS.