> When did something so significant happen that I became an "I"
Consciousness. The "think" part of "I think therefore I am". The part that makes humans human at all. Life experience. Presumably many years of it. You aren't even the same person you were yesterday let alone the cluster of cells that never experienced consciousness.
> I'm just the one organism, from all the way back then until now
Stopping there is arbitrary. If some rockslide hadn't happened a million years ago then your parents wouldn't have been born. It's causal chains and forking paths all the way down. How much do you debate the morality of rockslides? We have the power as a species to stop them now. Do we stop them? Do we never stop them? Both paths are genocide, just of different groups of people who will never be. Which group is the one we should choose to support?
I don't think we are talking about a difference of degrees. That's what makes me viscerally uncomfortable about it. If this tech had been commonplace when my parents decided they wanted to have a baby and conceived me, they would have had to look at this graded set of their offspring, one of which was me, and pick me out of the group--the group of...what? The group of other embryos basically just like me. Genetically speaking, my brothers and sisters. And then they pick me (or don't pick me!) and the rest just...die. Or languish, frozen, in case they chose one that didn't work out, or they want more later.
The ordinary process of IVF is weird enough to me. Adding this dystopian layer of trying to select for the best of your offspring based on genetic hypotheses about their future and disposing of the rest makes my skin crawl.
I mean that is great news when you get into the job market, right? Instead of 400 applicants for that job you need, only competing against 300 — dead babies don’t need to work!!!
Good. Done. Problem solved. We agree that we don't need to know exactly when it was to know when it definitely wasn't.
> Adding this dystopian layer of trying to select for the best of your offspring based on genetic hypotheses about their future
IMO you should stick with this part and forget about the embryo part. You can be worried about the process and outcomes of eugenics without focusing on any hypothetical unselected individual.
Not remotely. You provide no defense whatsoever of consciousness as a valid distinction between "you" and "not you yet," so it doesn't matter whether it's present at the beginning of your development or not. Whether one arbitrary feature you think is decisive is present at a particular point is completely irrelevant to anybody else, unless you can defend that that feature actually matters. I'm looking forward to hearing your case for it.
The undisputed reality is that every human adult was once a specific human embryo. "Embryo" is one stage of human development, just like "infant," "adolescent," or "adult."
There might be an argument for dismissing and eliminating certain embryonic humans en masse because of some trait they have or don't have, but you'd really need to pick one and make an argument for it, and it'd be a good idea to make sure the distinction doesn't apply to humans at other stages too if you don't want to have to argue that it'd be fine to kill toddlers, adolescents, or adults if they happened to have the same trait. It would probably also be important to make sure it's empirically verifiable, unless you're fine with whatever argument you make being used to justify killing toddlers, adolescents, or adults who might be thought to have/not have that trait.
But if such an argument does exist, you certainly haven't made it yet here.
> what level of consciousness matters?
We can start at least with the obvious distinction between "None at all" vs "Some" even if we don't know where the change happens. Asking "how much" only works if you want to investigate this dilemma within the "some" category, which we at least agree does not include embryos, and that embryos are in the "none at all" category. Investigating the "some" category strikes me as substantially more difficult because of that question about how much is enough.
For now, I say that "some" level of consciousness is required for mattering, which precludes a "none at all" level of consciousness from mattering.
Consider brain death. When a body becomes nothing more than a mass of tissue kept in motion by machine intervention without any brain activity, do we not say that it's ok for the family to decide to pull the plug? Because I say that it's ok to not keep brain dead patients on life support until the sun eventually explodes and the power runs out. But maybe you don't. And I understand that this is talking about an end rather than a beginning, but it's really just the other end of your question about how much consciousness matters. Clearly in that scenario the consensus answer is "at least some".
> There are severely disabled adults who have never been as "conscious" as some of the more advanced other animals. Do they just not count?
Question needed for me to establish a more shared understanding: Are you vegan? (I am not.)
If so, most people in the world are not, and that means if we're comparing to animals then clearly, at least en masse, we do discount lesser animal consciousness even if good vegans don't. But at least this framework would be consistent with a view that a threshold of human-level consciousness shouldn't matter.
If not, do you have a basis other than degrees of sapience for believing that a human embryo is worth worrying about but a chicken embryo is not that doesn't stem from egocentric instinctive queasiness? (I mean "egocentric" neutrally here, not negatively) Because the only other option I know of is "the <religious_book> says so", which is thought-terminating and we won't be able to move past that.
> If this tech had been commonplace when my parents decided they wanted to have a baby and conceived me, they would have had to look at this graded set of their offspring, one of which was me, and pick me out of the group
I get what you're saying but people actually already do this decision-making and have been doing so for a very long time. They just do it ahead of time by choosing who they reproduce with. Couples all over the world make decisions literally all the time about passing on negative potentially-heritable traits, from mild Autism to Scoliosis to Tay-Sachs.