I don't think that would have to be answered at all -- for the same reason that issues like cloning and euthanasia could still be addressed in Constitutional terms even though the Founders had nothing to say about these issues. Modern medicine, science, and technology has introduced a whole array of issues into our national politics that never came up in the 18th century simply because they didn't exist back then.
Black Americans today are entitled to full Constitutional protections even though the Founders specifically did not intend to protect them as "persons" under the Constitution.
Precisely.
That happened though a Constitutional amendment, not through a Supreme Court decision.
Technically, you are correct that the original Constitution did not give blacks (then slaves protections.
But, post-Civil War, there was an amendment to the Constitution specifically designed to protect blacks and a political US Supreme Court twisted the interpretation of the amendment in such a way as to unduly limit its protections to federal, and not individual state, actions.
Basically, the then-bigots of the US Supreme Courts took away the protections Congresss, the President, and 2/3 of the States gave blacks.
I believe this was the "Dred Scott" case, but I am no lawyer.
Can you point me to that clause in the Constitution?