What he's essentially doing is demanding that churches not stand for the truth of the gospel and is using tax exempt status as a way to control the church. There's no doubt that if this passed constitutional muster there would be any number of supposedly Bible believing churches banning their pastors from preaching on homosexuality in order to keep tax exempt status.
The Constitution can be interpreted not only for what is says, but also for what it omits!
Having seen Europe engulfed by religious wars for much of its history, the Founding Fathers made the conscious decision that the State would not align itself any particular religion!
While we taken religious freedom for granted in the 21stC, the creation of a new nation, without any mention of an official state sponsored religion in its constitution, would have been considered a revolutionary act by 18thC standards!
Separation of Church and State is not articulated in any form or manner within the text of the Constitution. Nor it is articulated in the text of the First Amendment. The First Amendment was crafted to keep government out of religion, not religion out of government. In addition it guarantees the freedom of religion, not freedom from religion. To claim the Constitution promotes separation of church and state by virtue of the fact it does not mention separation of church and state is a specious, puerile, and ignorant argument.
While we take religious freedom for granted in the 21stC, the creation of a new nation, without any mention of an official state sponsored religion in its constitution, would have been considered a revolutionary act by 18thC standards!