Certain objective safeguards must be established to ensure that Supreme Court nominees have fidelity to the Constitution. With our current system, a politically motivated activist can be added by a President who has no regard for the Constitution. Before being appointed, a Supreme Court nominee should have a record that proves fidelity to the Constitution.
If a judge has a record of decisions overturned by appellate courts, they should be disqualified from service on the Supreme Court. They should also have presided over a certain number of cases (that number to be determined through debate) that either have not been appealed or have been appealed and upheld by higher courts. A judge with fidelity to the Constitution will have made decisions that either were not appealed or were appealed and upheld. An activist judge will likely have their decisions overturned.
With these safeguards, an ambitious judge will lean towards staying well within the bounds of the Constitution if they have aspirations of higher office. Without these safeguards, an activist judge will push the limits of the Constitution (or outright ignore it) to gain the favor of a non-Constitutional activist President. Should the court be filled with non-Constitutional activist judges, the Constitution will be ignored, and we will regress into a state of tribalism.