Well, it not understandable that those who are affiliated with the army are angry at this decision? Bradley Manning exposed not only ‘the government’ or ‘the military’ as abstract entities, but also those acting on their behalf, namely each individual soldier. Put yourself in the shoes of someone returning home knowing that everybody has seen on TV what truly happens when US soldiers are deployed in faraway countries; the feeling of shame that this must bring about is quite unimaginable. It is only human to try to justify or hide whatever happened overseas; and fight its exposure to the fiercest extend - regardless of conventions, reason, moral codes, or oaths.
In the end, one thing speaks much louder than all controversy: the suicide rate of veterans, and the often diagnosed PTSD that comes from having acted against one’s deepest values. Seen in this context, and given the challenges the gay community still faces to this day a grand marshall that unifies rather than divides the community might have indeed been a wiser choice.