Yeah, that's correct. McCain killed a shitload of people. He was a soldier, he did his job. If that job is morally acceptable or not is certainly up for discussion, but it's not a revelation that he killed people in a war.
And if the best you can come up with to criticize him is "Oh, he killed people when he was a soldier", then maybe take a look at his record, where you'll find much more relevant and unambiguous things to be angry at him about, than "Dude did his job as a soldier in a war."
That said, I don't fault the dems(or independents, or Bernie in his weird in-between position) for applauding McCain for coming back to work, regardless of what he did with that return. They've all worked together for years, and what do you expect them to do, boo and jeer at the guy fighting brain cancer just because they know he's going to make a shitty decision? He's an asshole who is all talk, no walk, but he's still a person.