On Tuesday morning, a pro-abortion Twitter thread went viral. The thread posited a thought experiment the author claimed to be original, though it has existed in one form or another for over a decade (I first became aware of the thought experiment from Harvard philosopher Michael Sandel, who was arguing in favor of fetal stem cell research at the time). Here’s the hypothetical, according to one Patrick S. Tomlimson, comic and author of the ARK trilogy. Tomlinson’s scorn for the pro-life movement pours from his verbiage:

Let’s put aside Tomlinson’s obvious douchiness; the commenters on the Twitter thread are properly puzzled. That’s because Tomlinson is correct that we all have a moral instinct: to save the five-year-old. But he’s wrong if he thinks the hypothetical proves that embryos aren’t human life or potential human life, and therefore of no value. There are at least four reasons for that.

1. Moral Instinct Does Not Always Mean Correct Moral Decisionmaking. We all have the moral instinct to save the child. That does not mean that the instinct is either correct or justifiable. A few quick thought experiments suffice to prove the point.

Here’s another, more famous thought experiment: you’re standing at the fork in a track for a runaway trolley. On one side of the track is a man tied to the tracks; on the other side are five people. You choose to throw the switch to save the five people, presumably. But now comes the second part of the hypothetical: instead of standing at a fork, throwing a switch, you’re standing above a single track on a bridge. Five people are still tied to the track. Conveniently enough, there is a single fat woman standing atop the bridge with you. If you throw her in front of the train, you can stop the trolley before it hits the five people. Most people say they wouldn’t do it. Does that mean that the five people below are not humans, or that it is morally correct to avoid tossing the woman?

Or, say that instead of the box of random embryos, there are two embryos – and they are yours and your wife’s, your only potential children, and as in Tomlinson’s example, we know they will come to fruition. Your instinct could easily be to save the embryos rather than the five-year-old child. Would Tomlinson then say that the five-year-old isn’t a human?

Or let’s say that it was your five-year-old in the room, and next door were 1,000 actual full-grown human adults. Your instinct would probably be to save your five-year-old. Mine would be. Does that make me right, or the 1,000 humans no longer human?

2. Tomlinson’s Thought Experiment Does Not Reveal The Value Of Embryonic Life. We can agree with Tomlinson that one ought to save the five-year-old rather than the box of embryos and still not admit that embryonic life is meaningless. In fact, we can imagine scenarios where we choose the box precisely because we want to preserve human life. Here’s from Gregor Damschen and Dieter Schonecker at Universtat Halle-Wittenberg in response to Sandel: you’re in Tomlinson’s thought experiment, the embryos will grow into human beings using artificial means (as in Tomlinson’s thought experiment), but there are no other human beings. In fact, this is often the leading premise of science fiction. Do you save the five-year-old and doom the human species to extinction, or do you save the embryos? In this case, potential human life outweighs current human life. Does that mean the five-year-old is no longer a human being? Does it prove, according to Tomlinson, the value of embryonic life?

Here’s an easier one: you can save the box of embryos or you can save the life of a woman who will die of cancer tomorrow. Which one do you save? If you choose the embryos, is the cancer-ridden woman therefore of no moral value?

3. Most Pro-Lifers Freely Admit The Supreme Value of Already-Born Human Life, But That Doesn’t Make Prenatal Life Valueless. Virtually every religious system, including Catholic religious doctrine, allows passive abortion (the moral equivalent of this case) in order to save the life of the mother. Let’s say a woman has cancer and she requires chemo in order to cure it, but the chemo will result in the death of a fetus. There is no third option. Catholic doctrine suggests that the doctor bears no moral responsibility; the abortion is a byproduct of saving the woman’s life. So Tomlinson’s hard choice doesn’t remotely demonstrate the valuelessness of embryonic life.

4. The Hypothetical Isn’t Reality. This is the most obvious rebuttal to the implication Tomlinson draws from the hypothetical: the case of pro-abortion advocates isn’t a choice between a five-year-old and a thousand fetuses. It’s a case of killing a fetus, by itself. No such hard choice exists in 99.99 percent of abortion cases. Which means that using such a hypothetical to justify a doctor killing thousands of fetuses out of pure convenience is simply ridiculous.

Tomlinson’s initial thought experiment is interesting, but it doesn’t prove much beyond the fact that we make decisions all the time about the relative value of human life, often based on instinct. That doesn’t make our instincts right; it doesn’t justify non-hypothetical cases; it doesn’t even prove Tomlinson’s general point. But at least it allows Left-wingers to pour their instinctual scorn on conservatives without actually acknowledging the faultiness of their arguments.