Now imagine that the policy singled out any other religious belief for similar discrimination: that anyone could be a Scout who wasn't a practicing Roman Catholic, for example. That policy would arguably -- Eugene has convinced me of this -- be within the rights of a private group, and not subject to being overruled by state or federal civil rights laws. But the question whether that group should have free use of public facilities for its meetings, or extensive support from the United Way, would hardly arise. The group would instantly become disreputable, for the reasons Eugene lays out.
The policy in question wouldn't merely deprive individual Catholic kids of the benefits of Scouting; it would proclaim to the world, in a way that we as a people hold abhorrent, that there's something wrong with being a Catholic. Consequently, any support for the Boy Scouts, even the indirect support of giving them free places to meet, would be seen as supporting anti-Catholic bigotry. Putting the fact that one is an Eagle Scout on one's resume or college application would suddenly become a very dicey proposition.
The fact that the policy toward atheists is a real example, while the policy toward Catholics is a far-fetched hypothetical, merely points to the fact that this one kind of religious bigotry is still perfectly acceptable in polite company. (The polling data are appalling; atheists are the only group with net negative ratings in the Pew Center poll, rated unfavorably by about two-thirds of the public.) Senator Joseph Lieberman's denial that it was possible to have morality without religion was an insult to unbelievers that could not have been delivered with political safety to any other religious group.
Us godless people are fed up with religious bigotry.