The court did not decide whether the RFRA applied to all claims, merely the contraceptive claim. Therefore the appeal to authority falls flat on its face, because it is irrelevant that Kagan and Breyer did not join part of Ginsburg's dissent.

Ginsburg's dissent explicitly refers to the potential for the RFRA to apply in a more broad and damaging sense, and in that case Kagan and Breyer would almost assuredly agree. It's clear that they did not join that part of the dissent because they want to leave themselves open to future interpretations of the RFRA and how it is implemented. ie, say a corporation requires people to wear veils or something or only agree to a given religion, Kagan and Breyer could then go and be against it while maintaining the RFRA, but Ginsburg's dissent requires her to be against such an action, as she makes a blanket case against all for-profit corporations having that power.

The RFRA is not supposed to be discriminatory, ie, compelling people to act a certain way (in this case, you may not use your company provided insurance to pay for contraceptives). It was meant to allow for free exercise of religion so long as it did not harm other employees (so you couldn't invent a religion that allows you to scream at the top of your lungs for an hour a day in the library or something).

What Ginsburg is saying is that the RFRA is being applied in a broader corporate personhood sense, and of course, since Greenwald supports corporate personhood, he disagrees with her and wants us to read the conservative analysis.