David is correct to suggest that a firm is not being used to exercise religion merely because it has some religious people among its stockholders. If those individuals are a minority or even a majority that fails to get its principles embedded in corporate policy, then they are not using the corporation to exercise their religion – just as a corporation that has only a minority of stockholders who wish to boycott racist regimes is not being used to express antiracist principles. But that is just to say that corporate property, like any other property, is only used to exercise a constitutional right when the legally required proportion of its owners choose to use it in that way.
David seems to draw a distinction between speech (which he recognizes can be exercised through a corporation), and religion (which he thinks cannot be), because speech is “an inherently public act,” while religion is not. I think that takes too narrow a view of religion. For many religious people, their faith is not just a purely private hobby. It is rather a set of moral principles that infuses every aspect of their lives, including their activities in the commercial world. If atheists like me can use publicly traded corporations to pursue secular moral principles, it is not difficult to see how religious people can do the exact same thing with their own beliefs.
None of this proves that publicly traded corporations should always prevail when they assert religious exemptions under RFRA or under the First Amendment. But it does show that they should not be categorically barred from making such claims.