Good post, Jay. The Brian McLaren example you cite is chilling. That alone should disqualify him from leadership. (Thank God he wasn't around in 1940 to instruct Dietrich Bonhoeffer and Martin Neimoller on so-called single issues.)
Call me a simple man, but I've never understood the fascination with MacLaren and those like him.
First, given their belief we are trapped behind our own language communities and therefore can't know things as they really are, who in the heck are they to lecture us about anything--including our alleged need as Evangelicals to "change everything?" That is to say, how have they escaped their own language communities to tell us what's really true? Do McLaren, et al, think their views are true objectively or are they just constructs of their language communities? If the former, why can they get beyond language to see things as they really are but I can't? If the latter, why should I care what their language community thinks? Maybe I'm part of a different community and thus can't connect with their preaching. In short, I find their whole enterprise self-refuting.
Second, McLaren attacks a strawman when he says that foundationalism (the philosophical view that we can build our beliefs on a set of 'foundational' or basic beleifs) is dead because Christians don't have "bombproof" certainty for their basic truth claims. Since when do we need certainty to have genuine knowledge? I'll bet McLaren doesn't have "bombproof" certainty that his wife isn't having an affair with Michael Jackson, but does that mean he should doubt her fidelity? In the same way, Christians aren't required to have certainty before claiming their beliefs are true and reasonable to believe. They only need to demonstrate that their worldview is more plausible than alternative explanations. Thus, while I cannot prove God exists with bombproof certainty, it's still reasonable for me to say He exists provided the evidence for His existence is more compelling than the evidence against his existence.