But Herb, with Singer at his side, is fast approaching. They are looking at me, and Herb is talking, no doubt saying nice things about me. He'll be saying that I'm a disability rights lawyer and that I gave a talk against assisted suicide at his secular humanist group a while back. He didn't agree with everything I said, he'll say, but I was brilliant. Singer appears interested, engaged. I sit where I'm parked. Herb makes an introduction. Singer extends his hand.

I hesitate. I shouldn't shake hands with the Evil One. But he is Herb's guest, and I simply can't snub Herb's guest at the college where Herb teaches. Hereabouts, the rule is that if you're not prepared to shoot on sight, you have to be prepared to shake hands. I give Singer the three fingers on my right hand that still work. ''Good afternoon, Mr. Singer. I'm here for Not Dead Yet.'' I want to think he flinches just a little. Not Dead Yet did everything possible to disrupt his first week at Princeton. I sent a check to the fund for the 14 arrestees, who included comrades in power chairs. But if Singer flinches, he instantly recovers. He answers my questions about the lecture format. When he says he looks forward to an interesting exchange, he seems entirely sincere.

It is an interesting exchange. In the lecture hall that afternoon, Singer lays it all out. The ''illogic'' of allowing abortion but not infanticide, of allowing withdrawal of life support but not active killing. Applying the basic assumptions of preference utilitarianism, he spins out his bone-chilling argument for letting parents kill disabled babies and replace them with nondisabled babies who have a greater chance at happiness. It is all about allowing as many individuals as possible to fulfill as many of their preferences as possible.

As soon as he's done, I get the microphone and say I'd like to discuss selective infanticide. As a lawyer, I disagree with his jurisprudential assumptions. Logical inconsistency is not a sufficient reason to change the law. As an atheist, I object to his using religious terms (''the doctrine of the sanctity of human life'') to characterize his critics. Singer takes a note pad out of his pocket and jots down my points, apparently eager to take them on, and I proceed to the heart of my argument: that the presence or absence of a disability doesn't predict quality of life. I question his replacement-baby theory, with its assumption of ''other things equal,'' arguing that people are not fungible. I draw out a comparison of myself and my nondisabled brother Mac (the next-born after me), each of us with a combination of gifts and flaws so peculiar that we can't be measured on the same scale.

He responds to each point with clear and lucid counterarguments. He proceeds with the assumption that I am one of the people who might rightly have been killed at birth. He sticks to his guns, conceding just enough to show himself open-minded and flexible. We go back and forth for 10 long minutes. Even as I am horrified by what he says, and by the fact that I have been sucked into a civil discussion of whether I ought to exist, I can't help being dazzled by his verbal facility. He is so respectful, so free of condescension, so focused on the argument, that by the time the show is over, I'm not exactly angry with him. Yes, I am shaking, furious, enraged -- but it's for the big room, 200 of my fellow Charlestonians who have listened with polite interest, when in decency they should have run him out of town on a rail.

My encounter with Peter Singer merits a mention in my annual canned letter that December. I decide to send Singer a copy. In response, he sends me the nicest possible e-mail message. Dear Harriet (if he may) . . . Just back from Australia, where he's from. Agrees with my comments on the world situation. Supports my work against institutionalization. And then some pointed questions to clarify my views on selective infanticide.

I reply. Fine, call me Harriet, and I'll reciprocate in the interest of equality, though I'm accustomed to more formality. Skipping agreeable preambles, I answer his questions on disability-based infanticide and pose some of my own. Answers and more questions come back. Back and forth over several weeks it proceeds, an engaging discussion of baby killing, disability prejudice and related points of law and philosophy. Dear Harriet. Dear Peter.