He argues that the conservative versions of mainline denominations have several disadvantages:
- They usually lose most or all of the "institutional equity" (my term, not his) - think seminaries and their associated endowments, historic church buildings, name recognition from historical contributions to civil society - that the mainline denomination built up
- They usually abandon their liturgical roots and denominational distinctives and become generic low church Evangelicals
- They suffer moral injury because the liberals are the ones who have changed their beliefs, not the conservatives, so the liberals are the ones who should have to leave
Of these, I think the second point has the most legitimacy. All too often the conservative versions of mainline denominations completely trash their liturgy for some reason. What's conservative about replacing an altar with a praise band and a sleek podium? How can anyone who claims to value tradition throw out centuries-old hymns in favor of Hillsong? Why is it so common for the conservatives to get rid of their pews and replace them with folding chairs, or exchange vestments for a polo and skinny jeans, or put projector screens all over the sanctuary?
On who changed, it depends upon whether you look at specific beliefs or approach. Since the late 19th Cent, the mainline Presbyterian church has followed Biblical and theological scholarship. The conclusions aren't necessarily fixed, but the basic commitments are. Indeed many of the critical issues were already clear by the early 20th Cent in the fundamentalist controversy.
Since the fundamentalist controversy, the main new issues are gender and sex. But given the orientation of those who rejected fundamentalism, it was pretty obvious that they would accept women and gays as those became issues. There's a reason the conservative offshoots became a different sort of church. If RZ won, the PCUSA would as well. You can't maintain premises and change conclusions.
The nearest to what he wants is the ECO. They started out retaining all of the PCUSA confessions, even the recent ones, and looked like a body that was going to be similar to the PCUSA but with a conservative position on same-gender sex. My impression is that that hasn't been maintained. At some point you have to conclude that what he wants isn't possible: something just like a liberal church that is conservative on things he cares about.
But along with bbbbbb, I'm not so sure moving from specific Presbyterian tradition to generic is specific to either orientation. Protestants as a whole seem to be converging into generic Evangelicalism and mainline. I haven't seen nearby Presbyterian churches stop being Presbyterian, but outside the US, a lot of the denominations merged into united churches. We considered it in the US in the 1960's. I wonder if it will come back. The PCA seems determined to maintain traditional confessional Presbyterianism, even if a generic Evangelical spirit also affects them.
As to church equity, it's precisely with the institutions that change started: seminaries, national leaders and institutions. It's not like a few people managed to take over the church and force it on the seminaries. That's not likely to change, without a complete faculty change. Of course a conservative takeover could make that happen. We have the example of Concordia in the LCMS. But conservative takeover was a lot easier in the LCMS than the PCUSA, UMC, etc.