Complete apples and oranges - Foolishness -
The fact is there are plenty in differing fields of life that can read and understand what was meant by our Founding Fathers (that is part of the brilliance of what they put together!).
The idea that we need only people out of a specific field telling us what our Founding Fathers thought is not only ridiculous...but against the very concepts they supported.
You obviously have no idea what the Court does on a daily basis. Why don't you read the ERISA section of the tax code and tell me your opinion of whether the drafters intended it to preempt state law regarding reimbursement provisions of employee benefit plans?
Actually, I think you're right. There are a lot of people here on FR that show a keen understanding of constitutional law, much more than I, and it's my periodic hobby. I note that they're not lawyers, either.
I've talked with a number of lawyers and noticed that the general working lawyer knows very little about the constitution, even the one for his state.
Now, there are a lot of other knowledge and skills that would be necessary to be a judge, but that lack is covered by another legal profession, law clerks and paralegals.