Not a McCain fan but “merely doing one’s duty” when doing that duty means enduring immense suffering, rather than taking the easy way out is a form of heroism.
Of course it might not be quite as heroic as avoiding service with 5 deferments.
But it doesn't excuse that today he's the primary advocate of wars that have caused so much harm to so many, perhaps irreparable to civilization. I'd think a person who endured what he endured would not be advocating for the monster we've created in the Middle East.