Their argument goes a little something like this: "Your marginal utility from that second house/car/hundred thousand dollars is far less than the utility which would be gained by that person from it, therefore you owe him something.
Well, I'm going to propose that to them with another possession they might have two of, that some people have none of:
This is a kidney, it's a well-known fact that you can live with only one of them, but you probably have two nonetheless. As you're a left-winger, can you please explain to me why:
- It is morally wrong for me to make somebody sleep rough because I believe my right to the 14th bedroom of my mansion (I wish) is greater than his.
- It is morally acceptable for you to make somebody die because you believe your claim to your kidneys is greater than his.
This definitely passes the marginal utility test above. This guy is going to die if you don't give it to him, not just have to go without satellite television. You have approximately a 1% chance of developing end-stage renal disease, so his utility outweighs yours by at least a factor of 100 to 1.
Why are you not advocating forced redistribution of health?
Either you must accept that our claim to our own property is greater than the claim of others who so desire it, or you must accept that your ideology is incoherent, or you must all go and give a kidney away. Your choice.