At Movin’ Meat, Shadowfax has given a straightforward reasoning of single payor:
Before I launch into this, a couple of quick comments: First, I am not necessarily endorsing single payer as a national health plan. I do think it is probably one of, if not the, best systems possible for a nation-wide health funding system, but it does have drawbacks, as I will make clear, and is not itself a panacea. More importantly, it is a politically moribund proposal and I prefer to focus my thoughts on the possible rather than the ideal.
I encourage you to read it, as it’s very well done, even (especially) should you disagree with single payor plans.