This isn’t about agreeing with their sign, it is about the law that gives all of us our rights, be it Christian, Atheist, Buddhist, or Moonie. Those rights gives us our freedom to seek God, we can’t seek Him freely if we aren’t free in the first place. If we start banning other displays, we become no better than those who try to ban Christmas displays.
My point is not that these people don’t have the right to say it, but that government should not be expected to promote one religion bashing another. Might as well let the Klan put up an anti-Catholic display. I’m not in favor of vandalism, but the content of the sign puts it well outside the legitimate role of government.