ACLU sues over prayers at Cobb commission meetings

I wonder on what grounds the ACLU is suing? Certainly not on any constitutional grounds. As far as I know, the Georgia state constitution does not have any anti-religious language and the first amendment to the US constitution doesn't apply to Cobb County Commissioners.

Given that something like 90% of us believe in a higher being and that over two-thirds of us here in the good ol' US of A profess Christianity as our faith, why do we let the government pay the ACLU to engage in this kind of activity? Are we really that stupid?