Well two bits of dog dna combine to make a living being so what makes us different? I understand you’re an atheist or maybe just agnostic but something makes humans different. You could call it a soul if you want or find another word that expresses that essence.
Nah, dogs have a souls. What makes us different is our brain power/mental capacity. Everything else in us is found in other animals.
But not a unique life. Each is part of the father or mother. You want to argue for a woman's right to autonomy over her own body; there it is. Egg autonomy, not zygote, which is a different life from the mother.
You're obviously not familiar with what Roe v. Wade actually says. During the first trimester, governments could not prohibit abortions at all; during the second trimester, governments could require reasonable health regulations; during the third trimester, abortions could be prohibited entirely so long as the laws contained exceptions for cases when they were necessary to save the life or health of the mother.
If "thought" constitutes "life" then are you against keeping a comatose person alive with machines? If you think masturbation should be illegal, you agree with the "religious absurdity" (your words) of the Catholic church. I'm not equating embryos to adolescents, I'm making the point that both are developmental stages in the life of human beings. If you're arguing one has the right to life and not the other, make the leap and admit you approve of murder.
The specifics are debatable, but if your general argument is, if the mother is going to made to keep the baby, the father should be held legally responsible, I have no problem with that.