I'm not sure Snowden would be against it, if it stood a good chance of getting people talking about the upcoming reauthorization of the Patriot Act on June 1.
Considering it was intended to be a temporary art installation, the MIT Hacks reference seems appropriate: " It is a traditional courtesy to leave a note or even engineering drawings behind, as an aid to safe de-installation of a hack."-nightworks
The difference is that this was intended to be temporary and decisions were made to ensure safe removal, which I appreciate, but no instructions were left to a staff, possibly unfamiliar with the removal procedures, leading to risk of damage to the monument.
I also think it unfair to assume the victims for which the memorial was for would believe this is a valid usage - while the theme is close, the artists are equating Prisoners of War losing their life in a situation they had no control over ( at that point), versus a situation very much in the hands of snowden (ignoring the injustices, there are and have been many decision open to him). Having researched a bit more, equating the situation of a single person, to the thousands (~11,500) who were effectively murdered due to the inhumane conditions of their captivity is distasteful at best.
This is an opinion I know, and I appreciate this is a civil conversation if unpopular. I urge more reading on the memorial itself and its reason.
On a tangent, I think Jon's demeanor was a bit to jerkish for my taste. I appreciate the desire to not look like a softball interviewer, but some of his jokes and remarks and mannerisms were embarrassing either in its insult to Ed/Julian or in its pure unfunny character.