> everything that they will be when fully grown is contained there in that tiny little life

No, that's not true. Those two cells require a lot of care and nurturing and education before they become a person.

Have you heard of HeLa cells?

https://en.wikipedia.org/wiki/HeLa

They have a full compliment of human DNA, but no one in their right mind would argue that they are a person.

[UPDATE] This pithy slogan just occurred to me: a zygote is a person like a set of blueprints is a house.

They're as much a human as some living cells I shed on the floor. Alive and genetically human.

Being a person involves some level of thought, not just existing. If you ripped my brain completely out, and kept my body alive, most would consider the brain removal the time of death. That's when the person they knew died.

When you get a scrape and you bleed, thousands of your cells burst forth and die. Each has the same set of information necessary to rebuild an entire person. Have you committed mass murder?

The strongest arguments against abortion don't hinge on whether the fetus is a person. The question of abortion ultimately boils down to whose rights we privilege: those of the mother, or the fetus?

Heck, a sperm and an egg in separate containers have exactly the same information as a fertilized egg. That's a powerful argument for having a clear idea of what creates moral personhood.

Otherwise you're in the same camp that believes a sky daddy breathes a soul into your baby at conception and that IVF is the work of Satan.

In that case, it would also be a good argument against killing any single-celled organism, since it's a life that already exists. But life on Earth is cheap.

Are miscarriages then involuntary manslaughter?

There is a lot more to a person than genetic code. We are not IKEA chairs and DNA is not the assembly instructions.

Yeah?! You think so? Perhaps yours a strong argument against consumption of anything born this way, renders all meat consumption a bad thing with these same arguments… I bet 5€ you had your burger this morning and it had plenty of already dead cells in it, not to account for the yeast in the bread…

> From the moment the egg is fertilized, a new person exists.

The potential for a new person exists. Just as the potential for new people exist in a collection of sperm and egg cells.

The only difference, which you seem to be latching onto, is that now that potential has been turned into a more specific one. Why do you think that makes any real difference? It seems like an arbitrary and abstract argument that depends on an almost mystical perspective.

> This is a strong argument against abortion.

It really isn't. In fact, it's fallacious, because to accept the argument, you have to accept premises that produce the desired conclusion - i.e. it's question-begging, assuming its conclusion.

You are correct and for this: you are not going to be rewarded for it.

The cognitive dissonance is too strong, this entire subject should honestly be banned from HN.

It would be a so-so argument if it was true. (It is not) How DNA is expressed is a part of the story as well which involves many environmental factors both in utero and after birth.

We do not totally understand how it works, but there are heritable traits not passed via DNA - the one often in the news is women with emotional trauma pass that trauma on to their children, and those children show those symptoms even if raised in a happy home with 0 contact with the mother.

It is a philosophical argument, not a scientific one. One which if we try and reason based on how special nature treats embryos quickly falls apart anyways...