One of the perennial comments one hears is that if either A or B were correct "it is doubtful that so many Bible-believing, godly evangelical Christians would have wound up on each side." This flawed position assumes that "godly evangelical Christians" always tend to end up agreeing with correct positions.
That's a flawed assumption. In fact, "godly evangelical Christians" often disagree over things of lower consequence than the gospel. Take infant baptism as an example, or the proper ecclesiology.
What's worse is when people (such as Craig Blomberg) make the further leap of advocating something in-between those two positions as though this somehow bridged the gap created by the two positions.
In the case of Dr. Blomberg, the problem is worse because he's not actually adopted a position in the middle between Calvinism and Arminianism (the two positions he originally identified): he's adopted the Arminian position with a Molinistic explanation -- which is more like a halfway point between Calvinism and Open Theism, not between Calvinism and Arminianism. In fact, the "Arminian" position he identifies is that of William Lane Craig, one of the leading advocates for Molinism.
Even if Dr. Blomberg had actually picked something between Calvinism and Arminianism (rather than just picking Arminianism), what Dr. Blomberg has overlooked is that as soon as you set up a third position, the original argument still stands, only now there are three positions instead of two: three positions that "godly, Evangelical Christians" hold to. So the truth must be a fourth, and then (once people find that), a fifth, etc. ad infinitum.
Finally, Dr. Blomberg overlooks the fact that "godly evangelical Christians" disagree (mostly) with his fundamental premise that if "godly evangelical Christians" disagree about something, both sides must be wrong. This creates something of a paradox, since Dr. Blomberg must now rethink his original synthetic premise by synthesizing it with the position that "just because 'godly evangelical Christians' disagree about something doesn't mean both are wrong" position.
Truth is absolute, not relative. Just because "godly evangelical Christians" disagree about something doesn't mean both sides are wrong (or, necessarily, that either side is right). We need to continually go back to Scripture and let that (not counting heads) be our way of determining truth.
Thanks to Josh Walker for pointing this out to me.