Yes, the standard is vague. But at some level, all laws come back to moral judgments of one kind or another. Even if you start with practical concerns, you end with moral values.
For instance, why do we value free speech? Because we believe that free speech is a human right. This is a moral belief. If a dictator says "I don't believe free speech is a right," I might argue that society functions better with it.
But the dictator doesn't care how well society functions, in terms of outcomes for other people; he only cares about his own power. In the end, my argument would be that people have rights that "shouldn't", in a moral sense, be violated.
And that is exactly what the United States' founders said - "that all men are created equal, that they are endowed by their Creator with certain unalienable Rights..."
I don't think the moral judgement is always so easy to find, though. Look at the second amendment, for example:
A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed.
It should be pretty clear to any strict constitutionalist that what's being laid out there is not a moral, inherent right to carry arms but a means to an end. Yes, there is a moral judgement in that it's worth doing things to preserve a free state, but it's several times removed from the actual question being addressed.
For instance, why do we value free speech? Because we believe that free speech is a human right. This is a moral belief. If a dictator says "I don't believe free speech is a right," I might argue that society functions better with it.
But the dictator doesn't care how well society functions, in terms of outcomes for other people; he only cares about his own power. In the end, my argument would be that people have rights that "shouldn't", in a moral sense, be violated.
And that is exactly what the United States' founders said - "that all men are created equal, that they are endowed by their Creator with certain unalienable Rights..."