For a man consigned to that fate, he seemed to be content, if his smile was an indication of his feelings.
People look like that when their dead!
Seriously. WHERE is the trial?! And you know if you are gonna take a while to get the trial together (since all the witnesses are dead) you put a man in prison while you wait. So he can confer with is lawyers.
What sort of horror filled Federation is this.. OH A BAD MAN, FREEZE HIM!!
It does make him more of a woobie, though, which is good for fangirls and fanfiction writers everywhere.
But the decision is kind of WTF and I kept wondering why the hell everyone and their dog gets a trial, but Cumberkhan doesn't. Because he's TEH EVULZ. He did save Kirk's butt and got shot in the back for no good reason, but he's evulz and deserves to serve time as a (super)human popsicle.
I also think that demoting Kirk for exposing those natives to the Enterprise and accidentally creating new religion may have been a bit harsh.
However, seeing as they promoted him to captain after saving the Earth in the previous film, maybe that's how Starfleet rolls in JJ-verse.