First and foremost, the Constitution was never intended to be high-brow legal dissertation. It was, and still is, a document written in fairly common language and understandable to the common man. There are fairly simple concepts detailed within, recognizing certain God-given rights enjoyed by all men, and framing the appropriate relationship between the people and government. There is nothing about the document that is esoteric. It is exactly what it is. It certainly does not take a lawyer to understand the meaning.
Why then, does every Supreme Court nominee have to be a lawyer? The Consititution does not require a Supreme Court judge to have spent years pursuing a law degree, or endless hours in retentive legal pursuits at some high-powered law firm, to be a member of the Supreme Court. There are no specific requirements at all. In fact, at the time of the Constitution's drafting, many lawyers were self-taught men, who may have studied under another lawyer, but who likely did not have formal legal education. In any event, wisdom and common sense are not exclusive to lawyers, and today that profession often attracts individuals with neither. Lawyers also have the unfortunate tendency to become obsessed with legal precedent and the writings of other lawyers and judges, and in this world the convoluted examination of fairly simple concepts becomes and end unto itself. Using strict Constitutional principles, however, allows quick disposition of lower court precedents: If the decision is not based on what can be specifically read in the document, the decision is wrong, and must be rejected as unconstitutional. Examples of this are the mythical right to abortion, and any gun control law ever applied to a law-abiding citizen.
Interpreting the Constitution requires only one skill: The ability to read. Believing that only lawyers and judges can understand it is to deny the brilliant accessibility intended by those who wrote it in the first place.
Well, but what would a layman justice do with all the legalese dutifully produced by his/her and others' clerks? To sit here with an open mouth would be undignified, to rubberstamp their output would not look too good either. Thus we either need a constitutional convention which would produce a radically simpler document not open to interpretation, or we are stuck with professional lawyers.
There were no plumbers or seamstresses available who have constitutional law as a hobby.
It would be refreshing to have Spencer Tracy nominated. His common sense and plain-speaking would override his inability to handle the legalese.