Vengeance would be actively interfering to cause someone harm. Kicking an already dying man could be considered vengeance. Just allowing nature to take its course isn't enacting vengeance. Justice is in seeing someone pay in some way for their crimes in a proportional manner. Giving comfort to a dying man won't save his life, but rather ease their way out of it. Someone like Hitler denied millions of people that privilege, so it's justice that he too be denied it. Justice doesn't close wounds on its own, but it allows them to start healing. Deny justice and the wound festers. Doing something like conforting Hitler on his deathbed is a good way to delay the emotional healing of victims that have already suffered greatly. You're putting the immediate needs of a monster over the long- term challenges of anyone they hurt.
McCain has done shit things but he's nowhere near Hitler and likely believes that what he's doing is for the greater good. I'm not saying anyone has to feel bad for him being on his deathbed, but arguing that anyone who doesn't shit on him for being near death's door or hopes he doesn't die is being cowardly or aiding them in their shit goals is insane.
What's amazing is that, for all the hand-wringing on here about how disrespectful it is to be indifferent to this, the most jovial celebration of McCain's diagnosis appears to be coming from the far-right, who despise him way more than liberals who mock him for being spineless.
Seriously, though.