One reason: his apparent offhand equation of Muslims with terrorists. Another: encouraging students to show "them" a lesson if "they" ever showed up at Liberty. As my students well know, careful pronoun use is important. Who exactly are the "they" and "them"? Muslims, terrorists, or just any active shooter? It's not clear, and that's a problem. Someone with Falwell's platform and prominence can't afford to just toss words around lightly.
But Sarah Pulliam Bailey's Washington Post article on this topic included the following remarks of clarification from Falwell: “Jesus said ‘Render unto Caesar that which is Caesar’s,’ and part of that was to go to war, protecting whatever nation was under control of the king,” Falwell said. “I wouldn’t agree with any interpretation of Scripture that was used to say that a man or a woman shouldn’t protect their families.”
This last sentence is crucial, I think. The vast majority of Christians tend to agree with Falwell here. Liberal and conservative, Democrat and Republican, old and young. Presidents George W. Bush and Barack Obama certainly do. C. S. Lewis would. Many liberation theologians do. Complementarians and egalitarians do.
It's easy to attack Falwell's careless speech about Muslims. It's harder to attack what he said about the use of weapons to defend one's family and country (at least to do so consistently). Are all those who criticize Falwell willing to renounce the use of force to protect themselves and their families? Are they willing to condemn participation in war as not fitting for Christians? If not, it seems like there is some hypocrisy here. it's unclear if they merely have a problem with how Falwell made his point as opposed to the underlying substance of what was said.
There are a minority of Christians who would see the use of weapons, especially in war, as inconsistent with bearing witness to God's kingdom. God uses earthly rulers to keep things in check, but that's not the job of Christians. For those in this minority camp, the problem with Falwell's remarks is deeper. Self-preservation and the preservation of important things, even one's family, is not the end goal. Serving God's kingdom is. We can afford to lose our lives because we know that we can never truly lose our selves. God holds us no matter what may come. And the more we try to take our survival and self-preservation into our own hands, the more likely we'll really mess things up (see: Genesis 3).
So it's hardly surprising to hear someone at a University called "Liberty" (could there be a more stereotypical American name?) proclaim what most Americans take as the Gospel: that we live by the sword. Perhaps we should stop acting shocked, then, when so many of us die by the sword on a routine basis.