Easy to prove. When your rights are violated then something is taken away from you. If your action takes something away from someone else then it is not a right. Only those things which you can do or have that do not take away from others are your rights. This is, as the Declaration says, self-evident.Rights are man made and enforced. In nature there is no such thing as a right to free speech or a right to vote. If there is please ask your God to come down and show us those laws it created. The burden of proof is on you for claiming where our rights come from.
But what is the defining moment? By quoting the Constitution, you claim that it is basically which side of the vagina that you're on. But this argument is absurd because a baby that maybe was born 5 days ago was still viable. Even if born a few months early that are still viable with an incubator (are people on respirators necessarily dead?). So, we can see that the claim that just "being born" is absurd. This is not when we get our rights. So it must occur at some point in the womb. The onus is on you to prove when that is because it cannot be at birth.LEVEL OF DEVELOPMENT. I do not care about what potential it has to become a person. I care about what is a person and what isn't. A zygote is by no means a person, it has zero viability outside the fetus. I can't stress this enough.