Look, I emphatically believe in what Snowden did (though I may have some quibbles with his methods, his reasons were exemplary). I don't think that justifies what amounts to glorified — if tastefully done, and in keeping with the aesthetics of the monument — vandalism.
This is a war memorial. How might it feel to those who have lost loved ones in one of this country's innumerable wars, to have the monument to their loss, their sacrifice, appropriated for someone else's speech?