Steve, I agree with you up to a point--an execution would not have been in accord with today's values. 
 However I consider his crime extremely damaging to the US and would have preferred Life without parole.  Like you (and perhaps unlike those who as usual used this as an excuse for vilifying Obama and all Democrats) I served, in our military-  in our case, the USASA, with a top-secret crypto clearance, monitoring Soviet military activity.  Consequently I understand that Manning didn't just give away the contents of thousands of messages, but also, by matching these decoded messages with the one's they'd already intercepted, the Russians could easily break all our codes and read most everything we sent.
Steve, Putin may be Trump's buddy but he is no friend of America.  We live in greater danger because of Manning.