". the phrase that pops into my mind is: 'Preaching to the choir'"

Not so. FFRF is on the front lines protecting the Separation of Church and State
with law suits against the Religious Wrong. They're not preaching in any way but taking
a fighting stand against the religious zealots who want to subvert the Constitution
and turn the US into a theocracy.

I even think that fundamentalist, James Madison would applaud what they're doing.