Are Private Schools Still Legal in America? Is Promoting Legislation Still Legal in America?
I'd think the answer to all these questions would be "yes," even though the government generally declines to support these endeavors (and even though the government generally supports some similar or even rival endeavors, such as childbirth, public schooling, and speech on other issues). Many states ban the use of state funds or state facilities for abortion. The federal government provides a charitable tax exemption for contributions towards a wide range of advocacy — an exemption that is economically equivalent to a form of matching-grant subsidy — but excludes the express promotion of (or opposition to) candidates or legislative proposals. All these provisions are constitutional, and hardly raise the question "Is [X] Still Legal in America?" If anything, it's been conservatives (on the Court and among the public) that have generally argued that failing to subsidize behavior — even constitutionally protected behavior — is far removed from banning it.
Yet the rather conservative Washington Examiner runs the headline "Is Christianity still legal in America?" for a column that faults a public university for mandating that groups (including religious groups) not discriminate based on sexual orientation in choice of officers. I've written about why I think these policies are generally constitutional (though in my view often unwise), partly by analogy to the funding choices I described at the start of this post. The matter is made complex by the fact that sometimes the Court has held that the government must fund constitutionally protected behavior that it disapproves of; for instance, the government may not discriminate based on speakers' viewpoints in operating a broadly available funding program. I discuss that in my article, in more detail than you'll likely want, and come to the conclusion that exclusion of groups based on their expressive association choices doesn't fit within that relatively narrow exception to the "government need not fund behavior it dislikes rule."
But complex as the constitutional matter might be, one thing is simple: Government rules that all groups that get government benefits comply with certain restrictions — even restrictions that end up bearing especially hard on some Christian groups — aren't even close to making Christianity illegal; instead, it's a lot closer to the government's choosing which behavior (childbirth but not abortion, public schooling but not private schooling, much speech but not electioneering or lobbying) to support using its money and access to its property.
UPDATE: Silly screw-up in characterization of the lower court decision corrected (thanks to reader Jeremy Richey for alerting me to this) -- sorry about that; the substantive point remains the same.