“Peace if possible, truth at all costs!” Thus heralded Martin Luther half a millennium ago, and let no man accuse him of failing to practice what he preached. Of course, whether or not a Christian agrees with Luther’s particular interpretation of truth will determine whether he is a Catholic or a Protestant. But less obviously and perhaps more interestingly, whether or not a modern American agrees with Luther’s principle—that despite the very real goodness of peace, truth trumps it each and every time—will in large part determine whether he is a conservative or a liberal.The difference he sees is who values peace more and who values truth more. It is interesting but not quite accurate. Both liberals and conservatives value truth. That is just the way humans are wired. They cannot embrace something they believe is false or wrong. They can hold their nose and ignore things but they can't really fight for it. So everybody would agree with Luther's idea of truth at all costs. But the author himself qualifies it. Luther didn't fight for truth but for his "particular interpretation of truth." Hannon is looking for common ground between conservative Catholics and conservative protestants. He is suggesting the common ground is their love of truth. That is not it. The common ground is their certainty about truth. Conservative Catholics and conservative protestants are sure abortions, gay marriage, pornography, etc. are wrong.
Liberals are not so sure. In fact, liberals understand Martin Luther better. They get that he fought for "[my interpretation of] truth at all costs." They understand that everyone has an impulse to fight for what they think is right. They just are not sure who is right. They tend to believe the culture before they believe Christian tradition but they emphasize that nobody really knows. Conservatives think they know but they believe that is just because they don't get out much.
The truth is conservatives Catholics know that they know. Conservative protestants don't understand that Luther was a liberal. That they are defending a liberalism from another time that has passed into conservatism now. To understand that would raise the question of why liberalism was good then and it is not good now. The answer is it was never good. But to say that is to reject Luther and every protestant after him. It is easier to just not look at your own history so closely. It is easier but not very credible. Liberals point out how arbitrary conservatives are in saying this or that truth is solid and unchanging when they accept a lot of innovations from contraception in the 20th century back to divorce in the 16th century.
So the deeper link between conservative protestants and conservative Catholics is the belief that God gave us some bedrock truths that we must not question but simply obey. Liberals would be more inclined to say nothing is certain and everything is ultimately opinion. The question they ask is why this or that truth is bedrock. Protestants have trouble. They explicitly deny infallibility. That is what they are being asked. Is the immorality of abortion dogma? Should the consciences of all Christians be bound by that truth? Should those who deny it be considered to have left the faith? If you can't say that about abortion or any other controversial Christian doctrine then what do you say to a modern day Luther who's interpretation of the truth is different? All you can say is I think I am right and he is wrong and this is why. But you can debate until you are blue in the face and you will only end up proving the liberal's point that we don't really know for sure who is right.
Catholics confess that their faith includes infallible revelation from God. That those who disagree with the central tenants are forced to admit they can't affirm the dogmas of the faith. That means they reject the revelation Jesus Christ gave to the world. That is a revelation that has not changed. So we can argue that God's truth is objectively knowable. People can accept or reject Catholicism but they cannot say it is arbitrary or inconsistent. It flows from the acceptance of Jesus as the Word of God made flesh.
So the difference between protestants and Catholics does not come from "whether or not a Christian agrees with Luther’s particular interpretation" but rather it comes from whether one agrees that Luther had a right to a particular interpretation. What binds conservatives together is their belief in dogma. A consistent position for Catholics. An inconsistent belief for protestants. What binds liberals together is the denial of dogma. This time the protestants are being consistent and the Catholics are being inconsistent.