Thing is though, it seems you are making a _moral_ judgement there, not a purely clinical one. Strictly, triage would be kicking out the patient who had the lowest chance of survival even with treatment, not the one you had morally decided was least deserving. I think that's a different issue, and far more justifiable.
Once you start making moral judgements I'm uncomfortable with where that leads. Contrary to Juiblex's cheap gibe above, I see healthcare as a basic human right, including for Trumpists. I admit that in extreme situations, it might be very hard not to make moral judgments (which, come to think of it, is partly what Shaw's "The doctor's Dilemma" was about)
Edit - reminds me of the controversy over George Best's liver transplant. There's a difference between denying someone a liver transplant because of a judgement that it would be wasted because they would carry on drinking heavily and destroy it again, or denying it because of a moral judgement that someone wasn't deserving of a new one (donor livers being a scarce resource, much as ICU beds are now) because it was their own 'fault' they'd wrecked their original one.