From a safety perspective: It must be proven that the modification does not cause deformities, diseases, or effects that extend to future generations. This is a very difficult criterion because creating a new organ is extremely complex. From a benefit perspective: The organ is not a cure for a disease, so the justification for the risk is much weaker than modifying a gene to prevent a fatal illness. From the perspective of individual consent: If the modification is in an embryo, the person who will carry the modification did not choose it, and the modification may be passed on to their offspring. However, this does not necessarily mean the principle should be prohibited forever: If it becomes extremely safe in the future, there are no significant harms, and there is a legitimate reason and clear benefit, then its permissibility can be discussed.

You're treating uncertainty as if it automatically proves prohibition, but it doesn't. You say the core issue is that we lack the humility for this kind of power. Fine—but that's an argument for strict safety standards and limits, not an argument that the technology is inherently impermissible. Your conclusion requires showing that the risks cannot be reduced to an acceptable level, and you haven't shown that. You also keep appealing to irreversible consequences. But irreversibility alone is not a sufficient reason to prohibit something. Many decisions affecting future generations are irreversible. The relevant question is whether the expected benefits justify the risks under sufficiently strong evidence and safeguards. And the claim that this "normalizes the idea that some lives need engineering" is a slippery-slope argument. Treating a genetic disease or adding a particular trait does not logically entail that human beings should be engineered according to arbitrary standards. We can consistently distinguish therapy, enhancement, consent, safety, and coercion. Most importantly, you're arguing against a version of my position that I never defended. I did not say, "We should edit embryos now despite uncertainty." I explicitly said the opposite: the modification should only be considered if it becomes extremely safe, its consequences are understood, and there is a legitimate justification. So if your position is that human embryo editing should never be permitted, even if one day the modification were demonstrated to be safe, predictable, non-coercive, and beneficial, then you need an argument for that absolute prohibition. "Scientists might be wrong" is not enough. Otherwise you're not proving that the technology is wrong—you are simply saying that we should not use it until we have sufficient reason to trust it. And that's already compatible with my position.

You're making the same leap again: you're moving from "the future person cannot consent" to "therefore nobody has the right to make the decision." That conclusion doesn't follow. A child cannot consent to countless irreversible medical decisions made before they are born, yet we don't consider those decisions inherently illegitimate. The relevant question is whether the decision is made for the person's legitimate benefit, with an acceptable level of risk, not whether the person could sign a consent form before birth. You also say that even 99.999% safety leaves a risk for someone who had no say. But that argument proves far too much. Almost every medical intervention involving a child involves risk imposed on someone who cannot independently consent. The existence of risk creates a duty to justify and minimize it; it does not create an automatic prohibition. And you're treating "benefit" as if it inevitably means a slippery slope from curing disease to designing people however we want. That's not an argument; it's a prediction. We can establish boundaries: therapeutic interventions, non-therapeutic enhancements, coercion, safety thresholds, and heritable changes can all be regulated differently. The fact that one category might lead politically to another does not logically prove that the first category is wrong. Most importantly, you still haven't established your absolute principle. You say "not now, not in a hundred years." Why exactly? Suppose, hypothetically, that scientists eventually understand the relevant genes completely, the modification is demonstrated to have negligible risk, it causes no harm to descendants, the person is expected to benefit substantially, and there is no coercion. What morally relevant reason remains for an absolute ban? If your answer is simply "they didn't consent," then you're confusing lack of consent with lack of justification. A person can be unable to consent and a decision can still be justified on their behalf. So your argument successfully supports caution, extremely high safety standards, and strict regulation. It does not establish the much stronger claim that embryo editing should never be permitted under any circumstances. That's the claim you still need to prove.