Secularism (the political philosophy that advocates that church and state be separate and that people or all religions or no religion be equal in the eyes of the law) is the default position of the constitution and thus of American law. Since the constitution was signed, religious principles have never constitutionally been the default moral or legal foundations of the laws of the USA and its government -- it's a secular country. The six main founding fathers were enlightenment-era Deists, not Christians, and there is clear evidence of this in their letters, their communications, and in the constitution itself. THey didn't believe in enforcing religion on the populace, and they clearly recognized the need for secular principles.
The fact that a banner comes down, in alignment with these secular principles, does not change anything except to prove that these secular principles do exist, and have done, since the signing of the constitution. The world won't suddenly turn into horrible secular atheist humanists because a sign that violates the separation of church and state is removed. The world will still turn, just as it did yesterday, Crossnote.