Freedom to pursue your own religion, or even lack thereof, is not even a contestable idea. So - let a thousand flowers bloom, as the good Chairman used to say. If they want to split off and define their own church - fine.
But they don't want to split off and start their own church (at least the MCC crowd had that much integrity). They want to take off other folks churches.
Hmm. There's nothing in the article about anybody disputing their right to organize and define their own church; such a challenge is almost unthinkable in America. The burden of the discussion would not be, "Is it legal?" (assuredly it is) but "From the point of view of Christianity --- of which Lutheranism is a subset ---- is it right?