I think this guy hit the nail on the head.
I think it has to do with the dynamics of self-interest and self-deception. Some of the most virulent opponents of health reform are the elderly, who already have government-provided health insurance. While some may be too silly to know that that's what they have, a great many assuredly do know it, and are happy to pull up the ladder behind them. Medicare is already very successful and very generous. Under universal coverage, it's unlikely to get much better (except for prescription drug coverage, but not all the elderly take a huge number of pills). And it could, for all one knows, get worse. To avoid that risk, better that some youngsters go without.
This reasoning, though, is brutal--too brutal to acknowledge. While we're a pretty selfish country, "I'm all right, Jack" is not an argument people comfortably make when others' lives are at stake. But "if this passes, they'll euthanize me and my friends" is another kind of argument altogether. It's false, but easy to seize on as a morally comfortable pretext for opposing a bill that threatens one's self-interest.