Murder - illegal, has penalties. Same for stealing. Society has deemed these behaviors as detrimental/wrong and so have imposed laws. Society agrees with the worth of those commandments. Do the Ten Commandments stop there? No. There are others, of course.

What do you propose the legal penalties should be for these Commandments?:

You shall have no other gods before me.

You shall not make for yourself an image in the form of anything in heaven above or on the earth beneath or in the waters below.

You shall not misuse the name of the Lord your God, for the Lord will not hold anyone guiltless who misuses his name.

Remember the Sabbath day by keeping it holy.

Honor your father and your mother.

You shall not covet your neighbor’s house. You shall not covet your neighbor’s wife, or his male or female servant, his ox or donkey, or anything that belongs to your neighbor.

Are some commandments optional or not as important as others? Why are some commandments made into law but not others? Has the Biblical god stated that some are commandments but some are guidelines?

This really isn't about the destruction of Western civilization. An American ideal/Western ideal is the right of self-determination, of freedom of religious practice and the obvious subset of this the freedom from religious practice. Thus, the right of choice regarding religion is placed above the Biblical god's order to obey certain commandments.

This is what its really about (you said it yourself in your initial post):

"posting of the Ten Commandments for school children to learn"

That is fine for a parent who wishes that their child learn the Ten Commandments - as it is the right of all parents to decide their children's religious instruction without interference from outsiders/other parents.

You teach your children what you deem appropriate and good and wise and all of that kind of thing, and I will do the same for mine. And by respecting my right to decide what my children's religious education should be, you have every right to insist that I return the same respect to you.