I think what Icarus is saying is that it's possible the billboard companies refused to put up the billboard specifically because it was an atheist/freethinker group, which would be an issue.
If they did, I think they're entirely within their legal rights to do so. They can refuse to provide their service to any group as long as that group is not specifically protected from discrimination. I don't think atheists/freethinkers have that sort of protection. Perhaps somebody could build a case based on the idea that atheism is a religious belief (it's been done successfully before
), and therefore should be protected. It might be difficult because atheism, being merely a position on the existence of deities, is not promoting any positive beliefs unlike, say, Humanism.
Not clear if that's the case, since it was clearly designed to offend.
Exactly--this wouldn't be a test case I would choose if I were trying to show religious discrimination. The opposing legal team can argue that the company refused to display the proposed billboard because of its defamatory and inflammatory message. The billboard company could very well have decided not to display the billboard because they were justifiably afraid their property would be damaged or destroyed.
Our local Christian legal eagle might be able to provide more insight, or correct any errors in the above.