The Republicans (and sad to say, many Dems) in Congress oppose Obama's plans to close Gitmo because of the "dangerous" nature of its inmates (too dangerous for our maximum-security prisons). At the same time, these Republicans are urging Obama to support the Iranian demonstrators without reservation, ignoring the dangers of counterproductive U.S. support and its potential for igniting a new set of conflagrations in which Americans will die.
Then there's Mousavi himself. Is he more dangerous than your average Gitmo detainee? Perhaps:

As Iranian prime minister during the 1980s, Mousavi was linked by intelligence services to the 1983 bombing of a U.S. Marines barracks in Beirut, which killed 241 U.S. servicemen and prompted the Reagan administration to remove U.S. troops from Lebanon.