1. Sony is not a 'free speech platform' it's a multinational media company that produces films for profit. It is not their place (or their desire) to stand up for anything and they're certainly not going to take any risks with anybody's lives - that's for governments to do. Oh, and Sony certainly don't stand up for the 1st amendment or 'The American way of Life'; being a conglomerate of Japanese origins it's rather silly to call them 'Un-American' as some people in Hollywood have done.
2. Uncle Sam can do what about this exactly? North Korea may have been proven to be the source (as the media in the UK claims the US Government has now verified), but what exactly can the US do that they're not already doing? You think the US are not already involved in cyber attacks on competing ideologies?
It is disappointing that a film is withdrawn due to threats, but we cannot blame the media company who are just trying to mitigate their risk and losses. Blame North Korea all you like, but you can't blame Sony for being what they are.
I thought Sony's declaration that they will never release the film in any format ever was a mistake, though. They should have kept their options open.