Thanks for the overview, laconic. That is appalling. Very interesting tracing the problem back to the Vietnam era.
Before that, was Presbyterianism more akin to other Protestant faiths?
Yes, and all the other Protestant faiths (with the possible exception of the Unitarians) were closer to the Bible. All of the mainline Protestant churches are now extremely liberal; even the Southern Baptist Convention has tilted to the left.
PCUSA has been wildly liberal for a long time