Maybe I'm wrong or using false logic but isn't it a bit asinine to label the water your using "unholy water"?
If atheists do not believe in a god or any "higher power" then they do not believe in "blessed" objects which is what holy water essentially is. If objects cannot be blessed then they certainly cannot be "cursed" (if you will humor that opposing adjective) which means they contradict what they are doing by trying to be clever or cute.
I know they are just protesting and that's their right as well as their beliefs or lack there of, but in my opinion if your going to make such a public attack on another demographic (in this case a religious denomination) you should pay attention to the small details.
Obviously they were trying to get a reaction because if they truly did not believe in religion or "blessings" they would not care about the ritual performed and it would not bother them one bit that some religious group did something to some road awhile ago. Since they did choose to "troll" the real world and host an event to "undo the biased acts" of this church group, I find it amusing that they contradicted their own beliefs in their haste or possible obliviousness.