Activism in the Court dates most strongly to the Progressive era. But the Constitution stands above the positive law. Coolidge said it best IMO :
If all men are created equal, that is final. If they are endowed with inalienable rights, that is final. If governments derive their just powers from the consent of the governed, that is final. No advance, no progress can be made beyond these propositions. If anyone wishes to deny their truth or their soundness, the only direction in which he can proceed historically is not forward, but backward toward the time when there was no equality, no rights of the individual, no rule of the people.
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You mention the atrocious Brown decision. It should have been based on natural law, that a human is by virtue of being human a free person. But the Court took a rather wrong-headed approach:
During the “doll tests,” as they're now known, a majority of African-American children showed a preference for dolls with white skin instead of black ones—a consequence, the Clarks argued, of the pernicious effects of segregation. The Clarks' work, and their testimony in the underlying cases that became Brown v Board of Education
FURTHER, for many people, this brought even greater and more virulent discrimination against what was all black....Here is SCOTUS Clarence Thomas on that pernicious deduction:
[We cannot] “assume that anything that is predominantly black must be inferior.
