Using viability as the point on which to confer “human and civil” rights is arbitrary, which is exactly what you seem to be saying regarding how the Founding Fathers determined citizenship. You are making my argument for me. We later determined that the founding fathers were wrong allowing.

Arbitrary simply means there is no science to support the specific decision, but it is a matter of judgment (sometimes poor judgment as you rightly point out with slavery, given our country’s foundation was grounded on the idea that all men were created equal… and then we proceeded to undermine that belief).

The statement concerning viability is not an argument in favor of it or against it, but simply a statement of what the SCOTUS used to determine when an unborn baby was entitled to have the “state” protect his or her life. Such arbitrary legal decisions are quite common in our laws.

Why was 21 years, the voting age, prior to 1971. Then during the Vietnam War, it was reduced to 18 years. What was the scientific reason for the change? Did younger people suddenly become “smarter and more responsible”? The change was supported by those who felt someone old enough to fight in a war should vote, but was that same person not old enough to vote in World War 2?

Throughout our legal system, we use judgement to determine when something is age appropriate from what movies you can see, to what you can drink, or inhale. The specific age used is arbitrary, which is not the same as saying it is right or wrong.