Nope.
See, that's what people who focus on the wrong thing don't see there.
They're not attacking a god they don't believe in. They're attacking the fact that established religion has a greater say in EVERYTHING in this country---and it shouldn't. It's not attacking "god", who may or may not exist (I have my views, other people have theirs--I'm not debating the existence of any gods with you); they're attacking RELIGION. Big difference there.
Betcha the people that can't see the difference are the ones that thought the kids destroyed god at the end of the Phillip Pullman books (His Dark Materials), rather than killing the head of the church, which is really rather closer to what it was.
Anyway--if it's tilting at windmills to announce your beliefs, let's just get rid of the "god" in the Pledge of Allegiance, and on our money, and in our courtrooms. I mean, if God exists with or without that stuff, what difference does it make if you have it there or not? If you believe it, it doesn't matter if it's there or not, right?
To use your words---if it's "beating an empty sack" to be atheist and to state your beliefs, I guess that's what they have left after they dump out the beliefs from the sack that other religions--primarily the Christian religions (and I say that ONLY because I've never had any OTHER religion ask me to convert, whether I've found Jesus, told me arbitrarily that I'm going to hell, knocked on my door and asked to share their beliefs with me, handed me pamphlets, etc etc etc)--have shoved into their hands repeatedly. Maybe they're tired of holding a sack holding the imaginary friend of someone else. Maybe they're just trying to get the last of the dirt out of the sack so that they can use it for something other than belief?
Whatever it is, they have JUST AS MUCH RIGHT to their beliefs (or lack thereof) as your or I have to our beliefs. If one religious group (and I term atheists as a religion ONLY because it fits into the religious freedoms thing--I understand that it's a lack of belief in a higher being, rather than a belief "in" something) can put their beliefs/opinions/symbols on the public green, then every OTHER religion can put their beliefs/opinions/symbols on the public green too.
They weren't stopping anyone from practicing their beliefs. They were just putting an alternate point of view out there.