Ridiculous - that message is not “anti-God”. A free society by definition includes millions of non-believers, otherwise it’s a theocracy like Saudi Arabia, where being a “non-believer” is forbidden and punishable by death. That systems works great, huh? Ask yourselve why fellow citizens who simply don’t believe in God is so threatening to you.
Whose trying to stop them? We have already come up with a counter slogan for the billboard across the street.