^^I'm going to ignore your invitation to dumb down the conversation to a point you might feel more comfortable with. Your first example was of a government sponsored nativity scene, not christmas trees. There's a big difference between the two. Santa Claus, Christmas trees, holiday lights, etc. are "more cultural." Nativity scenes are specific to a religious celebration of the holiday. My family celebrates X-mas in a completely non-religious way, as do countless others...... just as we do with Easter eggs, bunnies, and baskets. I know more than a few Christians who celebrate Halloween.
FYI.... the ACLU is closed on Christmas - http://www.aclu.org/celebrating-christmas-america