From a strictly legal standpoint the principle of "substantive due process", which the Roe and Casey courts used to justify legal protections has very little basis in law or tradition. The concept is basically that the court can use substantive due process to protect a right that is not specifically enumerated by the constitution. In practice, it's some left wing bullshit to justify the Court making up new rights out of whole cloth. It has also been popular when the SCOTUS feels like playing JV legislature and decides a political question that should be decided by Congress. It gets trotted out when they can't shoe horn a decision into some other constitutional provision like equal protection.