Look, folks, if we want to show Christians that it’s not cool to vandalize atheist billboards (for example), the way to do it is definitely NOT to fucking spray-paint pro-atheist slogans on the sides of a CHURCH, for Pete’s sake.
That said, I’m a little skeptical that the vandals in this case were actually atheists. To wit:

Do you see what’s out of place here? I do not recall ever seeing an atheist person misspell the word “atheist.” I do, however, regularly see theist persons use that misspelling.
It’s possible that the vandals were members of a different denomination who wanted to fuck with Shady Grove United Methodist Church and pin it on the godless. It’s also possible that the vandals were some bored teenagers who attend Shady Grove United Methodist and decided it would be fun to spray-paint badly-executed atheist messages on the outside walls because they had absolutely nothing else to do with their time. (I’ve been in the Peace Corps; I don’t underestimate the depths to which bored teenagers will descend.)
It’s also possible that some atheists simply can’t spell. Then again, it’s interesting that they can spell “delusion” correctly but make a rookie mistake with “atheism.”
Of course, the red misspelled “atheism” might not have been the work of the same person as the others.
I’m paying a lot of attention to spelling, here.
Either way, I think that decent people of all strains of belief can agree that vandalizing someone else’s property is not okay.

