>If you come to my house I'll happily call an ambulance for you.

And I'd do the same. My objection is that my tax obligation is roughly the GDP per capita - that's well above and beyond calling an ambulance. What are the limits of what you'd do for me? Could I come into your kitchen and eat until I'm full? Could I play your video games if I were bored? Could I ask for a sexual favor?

>We have enough collective resources to treat the life-threatening illness of everyone within our borders

Why stop at the borders? Is the inside the border / outside the border distinction more ethical than the illegal vs non-illegal distinction?