It's hard to be sympathetic to former US Representative Cynthia McKinney. Among her achievements are putting forth the "Tupac Shakur Records Act" and being the sole member of the US Congress (as far as I know) to accuse Bush of having foreknowledge of the 9/11 attacks. After Hurricane Katrina, she took up the cause of an anonymous source who alleged that the Defense Department took advantage of the chaos after Katrina to dispose of 1,000 prisoners, whose bodies were "crushed by tanks, shot in the head, painted blue, and dumped in a Louisiana swamp."
That having been said, it seems that she's spot on in her criticism of the US military for turning back well-established humanitarian groups and even sovereign nations as they try to enter Haiti's ports and provide vitally important and time sensitive food, water, and medicine:
Every plane of humanitarian assistance that is turned away by the U.S. military (so far from CARICOM, the Caribbean Community, Médecins Sans Frontières, Brazil, France, Italy and even the U.S. Red Cross) – as was done in the wake of Hurricane Katrina – and the expected arrival on this very day of up to 10,000 U.S. troops, are lasting reminders of the existential threat that now looms over the valiant, proud people and the Republic of Haiti.
Where exactly, in any law on the books or constitution of either Haiti or the United States, does it say that the US military has the authority to deny planes and boats entry to Haiti?
Tyler Cowen also links to an Al Jazeera piece about a brewing showdown between the US and Brazil over who runs what in Haiti.