"'Congress shall make no law respecting an institution of religion.' -- The First Amendment to the Constitution
A Nativity scene (or a Menorah for that matter) is not a law, it is a decoration. And on that basis, even though I myself am an atheist, I do not have a problem with Nativity scenes on government property, other than they are a reminder that those are the people we are bombing to steal their oil.
I do draw the line at the Ten Commandments being on display on government buildings with its prohibitions against lying, theft, and killing, as that hostile work environment!" -- Michael Rivero