Thank you.
I believe that all law beings with some kind of moral judgement. Laws against murder are, for instance, not something that has always been universal throughout history. In many times and places, a person of higher status could kill a person of lower status with virtual impugnity, and "the law" didn't care. Making murder illegal is a moral judgement. Most laws are moral judgements of some sort, because someone believed it was "the right thing to do" for some reason. (Those "reasons" could be based on any number of personal biases, too.)
If the baseline for law is not to be in any way based on the morality of the large majority of the population... that is to say what the supermajority agree is right/fair/just... then what shall we base it on? Philosophy? That is simply religion with Reason in place of a god. Lots of philosophies wander far out into the wild places.... look at Sophistry for instance. Ideology? Well, that's politics, you can guarantee that's in the mix.
The Constitution? In my opinion yes, but the C was never intended to be a comprehensive codex of what should and should not be legal. 99% of that was actually supposed to be up to the States, originally.
Part of my point is that "moral" does not automatically mean "religion". People can have a moral code based on something other than religion. Whether someone's morals are religious-based or based on something else, I guarantee you their morals affect the way they vote. Excluding all morality from law seems most impractical.