Your argument is specious. Slavery was not the reason that led to a Civil War. It was the act of secession that led to that war.
Fred Thompson is not avocating secession.
As for the preamble, there is no mention of a right to life as there is in the Declaration of Independence. In the formation of the United States, it can be safely inferred that no one would have ever thought of killing a child in the womb. The right to life was left out because of the authority given for capital crimes.
So your slavery-abortion analogy is flawed.
The states can decide for themselves what there policy should be regarding abortion. However, should any state that generally outlaws abortion make an arrest of any abortionist or participant to abortion, there is no recourse if Roe vs. Wade is overturned. Because there is still a majority or at least a plurality of Americans in most states that oppose abortion, it is expected that most every state will outlaw abortion if not restrict it to extreme cases.
The US Constitution does not cover abortion, the Confederacy never addressed abortion, your argument is specious.
FDT is a federalist. His view on abortion is a federalist view.