OK: I'll bite.
On the one hand, Preston is right, as far as he goes: the NT certainly does not teach anything about Christian jihad against the world in spite of some important military metaphors built into Paul's rhetoric (we can talk about those some other time, or maybe in the meta). But it's factually true that Christians did commit Holy War against Islam the last time the Mussulmen were inside the doorstep of the West, and took it all the way to Jerusalem in the name of the Cross and Christendom.
But even in that set of facts, Instapundit is warning us not of external, ministry-of-the-sword kind of warfare: he's warning us about (for example) people who, in the name of Christ, will fire sniper rifles at abortion doctors. His specific example is, in fact, right-to-life advocates who take a militant view of the problem -- not just in a "church militant" way, but in a "second-amendment, right-to-oppose-bad-government" kind of way.
And while I have sympathy for Preston's rejoiner, I think he doesn't understand Reynolds' view at all, and understands the Christian right only in a Pollyanna sort of way. And before I say another word, let me make something as transparent as possible: I am a member of the Christian right. I haven't voted non-Republican since the 1980's, and the truth be told I can't see voting non-Republican in the next 15 years due to the state of blue-state politics in the country. So as I type out my opinion here, don't knee-jerk a response to what I'm saying.
And what I am saying is this: the SBC resolution against alcohol is the kind of intellectual capital which encourages this kind of thinking in non-believers. Pat Robertson's ridiculous and un-denounced prophecies and ravings inspire this kind of fear in non-believers. "Christians" who mail death threats to bloggers, or make vulgar phone calls, defame the rest of us in a way that causes those on the outside to know that the only thing missing for these kinds of people is means and a clear path.
I wouldn't dismiss Instapundit's fears or concerns very quickly. Yes: he is wrong about actual disciples of Christ because he thinks anyone who has a Christian bumper sticker on his car is a Christian. But let's ask ourselves something: does a response like Bryan Preston's actually refute the concern -- or does it ignore the causes of the concern for the sake of keeping a straight face in a public conversation?
Seriously: I want you to think about something by way of podcast. The White Horse Inn had a great broadcast two sundays ago, and I want you to listen to it, and think about the criticisms that these guys discuss. Isn't the logical conclusion of what they are talking about here Christians who are not concerned with Christ at all? And if the question of "team play" is what becomes the defining matter, what prevents us from playing to win using the rules the other guys have already established?
Think about this, people: when I say that the Gospel is the solution to Culture, this is what I'm talking about. If the Gospel makes us just like some other culture, then what exactly did Jesus die for?