Freedom of religion is all about - and has always been about - the state not persecuting people on the basis that they fail to adopt the state's preferred religion.
This is certainly one of the things that freedom of religion "has always been about" but it's hardly what it is "all about" and no one who actually took the history of the concept seriously could say it is. To take just one example, it's a standard feature of freedom of religion provisions almost everywhere to provide explicit protection of individuals from religious discrimination, and this is rarely if ever regarded as solely applying to states. One is reminded of the concluding document of the 1986 Vienna convention, whose very first provision on the topic of religious freedom is to insist that states "take effective measures to prevent and eliminate discrimination against individuals or communities on the grounds of religion or belief in the recognition, exercise and enjoyment of human rights and fundamental freedoms in all fields of civil, political, economic, social and cultural life, and to ensure the effective equality between believers and non-believers" -- rather excessive if the point is merely "the state not persecuting people on the basis that they fail to adopt the state's preferred religion"; and even if that weren't so, the very next provision is for states to "foster a climate of mutual tolerance and respect between believers of different communities as well as between believers and non-believers." There is no way to fit such a provision into Blackford's arbitrarily narrow definition of freedom of religion. And, indeed, it is notable that there is plenty for which Blackford cannot account: anti-discrimination provisions, in which religion is one of the protected areas, in housing, employment, and education, where those go beyond restrictions on the state alone.
And this hardly covers the whole of what people have discussed under the subject of freedom of religion; it's just that aspect of it with legal ramifications. But no significant freedom consists merely in legal protections; and, indeed, Blackford's restriction makes nonsense of one of the longstanding commonplaces about freedom of religion for the past several hundred years, namely, that it is a form of freedom of conscience. Now, virtually nobody thinks that freedom of conscience consists merely in protection from state persecution; if nothing else, this would be to confuse the protection with the thing protected. Freedom of conscience as it has often been taken is, as it would have once been put, a right and property from God, i.e., it is something we have prior to and regardless of any obligation pertaining to the state; it has not generally been taken, as Blackford would have to say it has, as simply a restriction on the state, but as something we restrict the power of the state in order to protect -- again, among the other things we do to secure it.
The point here, of course, is not that O'Neill's original argument was particularly stellar, nor that there can't be good-quality objections to it; indeed, I think she does much the same as Blackford, just without looking quite so foolish. Rather, the point is that one should not lambast people for ignorance of the meaning of certain phrases, when you are defending this claim by arbitrarily redefining the phrases involved. Rightly or wrongly, 'freedom of religion' even in the purely legal realm has quite often been regarded as going beyond the restriction of state power to the imposition of rules or procedures of tolerance among citizens. And when we move from the actual legal realm, then obviously more colloquial and expansive meanings will be given to widely recognized phrases; one thinks, as an analogy, of the extraordinarily expansive meaning Canadians typically give to the meaning 'sovereignty', which goes well beyond what its strict meaning has been, historically or in present international jurisprudence. These things may drive one crazy, and, if the confusions that come about from it are serious enough, one may reasonably set out to reform usage; but one should never pretend that this isn't exactly what you are doing, actively trying to reform, which is not a matter of knowledge or ignorance but a matter of the most appropriate means to whatever ends are most appropriate. We find that the problem comes up a great deal with 'freedom of speech'; and no doubt there are people who will argue that 'freedom of speech' should only be restricted to what is protected by restrictions on state power to regulate speech. But when we move to more colloquial ground, the meaning is simply not so narrow. We may be driven crazy by the sloppiness with which the term is used; but it makes no sense to complain that people who are using it in this way are using it ignorantly or confusedly just because they don't confine themselves to questions of state power.
It reminds me of the pedanticism of those people who mock people who use 'literally' as an intensifier for not knowing what the word means. Now, it's entirely reasonable to campaign against this usage as excessively confusing, or sloppy, or ugly, or what have you; but it's simply not reasonable to attack it as wrong, since that exhibits ignorance of the actual history of the term: the intensifier usage is in fact longstanding and is a usage that puts one in good company since a large number of classic authors use it; moreover, the usual meaning that is put in opposition to it, that which opposes 'literally' to 'figuratively', is not the only meaning the phrase has had, nor has it always been the dominant meaning. Nor is it anything but nonsense to regard one's campaign to reform the language as somehow not reforming at all but simply overthrowing all the false pretenders to the throne of meaning, leaving the perpetual and obvious true pretender in its rightful place. The most one is really doing is putting forward a proposal for what one sees as an improved use of language; and this is no rational basis for calling someone else ignorant or confused. They might well be ignorant or confused; difficult as it may be to countenance, that someone uses a term in a more expansive or narrow sense than you do does not show this, unless they are trying precisley to use it in the sense you use it and are failing. And even then it does not guarantee any such thing; it might just be inadvertence or sloppiness rather than real ignorance or confusion.
This can actually be fairly difficult; almost everyone finds usages that simply drive them crazy. And it's sometimes difficult to draw the lines properly; we move so easily from words to things and back again. But one might also say, just as a perhaps, that even if we give in to the urge to vent on these points (and it is possibly only human), one should avoid attacking people for "putting on airs" as if they were experts while telegraphing so obviously at every point that one is, oneself, merely putting on airs as if one were an expert.
UPDATE: Chris Schoen beat me to the punch with regard to Blackford's post.