Well the Constitution has two clauses. Congress can "make no law" respecting an establishment of religion OR prohibit its free exercise.

Your comment speaks more to the first clause (freedom from religion), whereas my article speaks more to the second clause (freedom of religion).

They are somewhat related though, especially in that whatever they mean depends on how we actually define "religion". And the fact that the Constitution does not define "religion" is one of the things that makes these conversation so hard.

I always thought the first clause was kind of impossible to put into practice though, because it's only natural for Christians to vote based on their Christian values, and Muslims to vote based on the values derived from Islam, etc. So even if a given law doesn't say it's in place "because of Christianity", in fact every law that we ever make will ultimately represent some manifestation of the religions of the people who made it.

So in the end, the important thing isn't so much whether a law reflects an establishment of religion or not, but whether it represents a good way of thinking or not. which is to say, whether it represents a belief system that has people's best interest in mind.