IMHO, Amtrak's attempts to wash its hands off all responsibility is shameful. But I guess as a legal strategy, it is what it is.
But the possible memes that can come out of this on the likes of Facebook is pretty alarming, if some anti-Amtrak entity gets hold of this and decides to run with it. It could be a public relations disaster. Much worse nightmare than say what United faced with the guy who was dragged off the plane.
This SHOULD be a public relations disaster for Amtrak, if their attitude to assaults on passengers on their trains is effectively "sh** happens, not our fault."
Common carriers are held to a higher standard of care because passengers are utterly reliant on them for safety and security while on board. ALL of Amtrak's onboard staff need to be trained to be vigilant for episodes of assault, and to treat responding to any such event as a top priority: make sure the passenger is OK, and make sure any alleged perpetrator is immediately isolated from other passengers. By "vigilant" I mean routinely keeping an eye out for circumstances that seem "off" and following up to make sure everyone is OK, instead of following the natural inclination to treat anything out of the way as interference with doing one's job.
Amtrak also needs to do a better job communicating to passengers that if they encounter any personal threat they can and should approach ANY Amtrak staff to report the problem. If they can do this for the extremely rare problem of terrorist activity ("if you see something, say something"), surely they can do something similar for the much more common problem of assault.
And, yeah, they do need armrests between passengers, especially on overnight trains.