The phrase "designer baby" is a slogan rather than a category. It collapses several distinct interventions—preimplantation genetic diagnosis for serious disease, polygenic embryo selection for common conditions, mitochondrial replacement, somatic gene therapy on a born child, and germline editing that alters heritable DNA—into a single rhetorical object. The collective task is not to defend or attack the slogan but to redraw the actual lines: which interventions are continuous with existing medicine, which constitute a categorical break, and which sit in the contested middle.
The line that the international scientific community attempted to draw after the He Jiankui scandal of 2018—when a Chinese researcher edited the germlines of twin embryos to disable CCR5 and brought them to birth—was that heritable germline modification is currently off-limits, not because the underlying capacity is irretrievable but because the safety, consent, and equity frameworks do not exist. That line is unstable. It rests on a moratorium that has no enforcement mechanism, on national regulations that diverge sharply, and on a professional consensus that has already begun to fragment as CRISPR-based therapies for sickle cell disease have been approved for somatic use and the distance between somatic and germline shrinks in the public imagination.
A useful way to draw lines is by asking who consents and what is heritable. A somatic intervention on a born child can, in principle, be consented to by the child as they mature, and its effects are limited to that body. A germline intervention is consented to by the parents on behalf of a person who does not yet exist and whose descendants will also inherit the change. The asymmetry is moral, not just technical: germline editing extends parental authority into generations of people who cannot push back. This is not by itself a prohibition—parents extend their decisions into the future constantly—but it raises the threshold of justification.
The case for some germline interventions is real. Eliminating Huntington's disease from a family lineage, preventing the recurrence of a known catastrophic mitochondrial disorder, removing a BRCA1 founder mutation that has caused generations of cancer—each of these can be argued for on the same logic that justifies any preventive medicine. The case against most germline interventions is also real. Enhancement edits—for height, cognitive traits, longevity—operate on systems whose biology is poorly understood, whose off-target effects cannot be confidently predicted, and whose social consequences would extend across class lines in ways the technology itself cannot remediate.
The line drawn by Michael Sandel and others is not primarily about safety. It is about the disposition that selection cultivates in parents and societies: the move from receiving children to producing them, from gift to product. This argument has force even when divorced from theological framing because it locates the problem in the parent-child relationship rather than in the technology itself. A society that becomes comfortable specifying its children loses something whether or not the specifications work.
The counterargument, developed by Savulescu and others, is that we already specify children—through schooling, nutrition, environment, even mate selection—and that the moral consistency runs the other way: if parental shaping is permissible after birth, it is hard to see why it becomes impermissible before conception. The honest response is that the discontinuity is real even if it cannot be fully justified by first principles. Most moral frameworks recognize that the conditions of a person's coming into existence are not equivalent to the conditions of their ongoing life. Drawing the line at the boundary of conception is partly arbitrary and partly the kind of principled arbitrariness that legal and ethical systems require to function.
Where the line actually gets drawn will be decided not by philosophers but by the interaction of clinical practice, national regulation, international agreements, and the consumer market for fertility services. The sixth law asks whether the line will be redrawn deliberately or by accumulation. The pattern so far suggests accumulation: each new application normalizes the last, and the moratorium holds only because no one has yet found a sufficiently sympathetic case to break it publicly. When that case arrives—a couple with a devastating inherited disorder and a clinical team willing to act—the consensus will be tested. The collective work of preparing for that moment, by deciding now what genuinely warrants germline intervention and what does not, is the work that is being deferred.