As a Libertarian/Voluntaryist I would like to respectfully present a differing reason for embracing the ideals/law of the Constitution.
My reasons for being "into Liberty" derive from two primary sources:
(1) Self-ownership; and
Why not morality and/or religion? Both are subjective. Who's morality? Who's religion? And that is just the tip of the iceberg. I'm not qualified or interested in talking about religion so I'm going to leave that one for now and say a few things about morality.
And yes, morality is the refuge of many liberals, progressives, conservatives, and even some Libertarians, sadly.
On the left you have, generally, people accused of "having no morals" or "having shifting or weak morals" because they will defend a person's right to do what they want with their body, spirituality, etc. while not caring about a person's right to their own property. But at the same time, the modern liberal or progressive will claim we all have a "moral obligation" to the poor or otherwise needy. So yes, the left do have morals; their own, which tend to rest on the ideology that force is OK when the goal is to create equality of resource distribution.
Those on the right are no more consistent. They will defend your right to do with your property as you wish but oh it is "immoral" to be gay, consume specific substances, have abortions, or be an atheist. So in their case, force is OK when the goal is to create security, whether that safety be for your soul, your body, or your land.
Neither has a consistent, integrated approach like the Libertarian and I call that "principled". But sadly, yes, many Libertarians subscribe to or believe our freedoms come from morality that came from God and/or the Constitution and/or some unwritten rule. It is shaky ground to stand on because it is subjective. No one has the same morals. But if you base your politics on a PRINCIPLE such as "I own me and thus no one else can" then, for example, right off the bat you do away with any "crime" that is without a victim because you own yourself and thus are free to do what you want to yourself.
I believe "morality" to be at the source of much of human-kind's problems. It is part of what I call "domination language." We all learn to speak this language from birth, and in so doing, our alienation from each other happens completely out of awareness. We accept our loneliness as being the natural state, when it really is not. This insight regarding language is only the tip of an iceberg. The language we are taught prepares us to live in a domination system where a few people will control the large majority and where we are encouraged to play the "Who's right" game. Words like "right" and "wrong" make it easy.
I value freedom. This statement is a value judgement, to be distinguished from a moralistic judgement which implies right or wrong. Freedom means I take responsibility for my choices because I choose to do the things I do. The problem is we are taught from an early age that we are not free, despite words to the contrary. Domination systems want to fool you into believing you are free, yet have you all the while serving them. In actuality, "You are free, but you just don't know it!"
You can also check out this article I wrote on the topic of moral judgement