Suppose you're a protestant, and you want to convince other people to do what the Bible says to do. Would you persuade them by showing them that the Bible says that they should?
Now suppose you're a rationalist, and you want to convince other people to be rational. Would you persuade them with a rational argument?
If not, how?
ADDED: I'm not talking about persuading others who already accept reason as final arbiter to adopt Bayesian principles, or anything like that. I mean persuading Joe on the street who does whatever feels good, and feels pretty good about that. Or a doctor of philosophy who believes that truth is relative and reason is a social construct. Or a Christian who believes that the Bible is God's Word, and things that contradict the Bible must be false.
Christians don't place a whole set of the population off-limits and say, "These people are unreachable; their paradigms are too different." They go after everyone. There is no class of people whom they are unsuccessful with.
Saying that we have to play by a set of self-imposed rules in the competition for the minds of humanity, while our competitors don't, means we will lose. And isn't rationality about winning?
ADDED: People are missing the point that the situation is symmetrical for religious evangelists. For them to step outside of their worldview, and use reason to gain converts, is as epistemically dangerous for them, as it is for us to gain converts using something other than reason. Contemporary Christians consider themselves on good terms with reason; but if you look back in history, you'll find that many of the famous and influential Christian theologians (starting with Paul) made explicit warnings against the temptation of reason. The proceedings from Galileo's trial contain some choice bits on the relation between reason and faith.
Using all sorts of persuasive techniques that are not grounded in religious truth, and hence are epistemically repulsive to them and corrosive to their belief system, has proven a winning strategy for all religions. It's a compromise; but these compromises did not weaken those religions. They made them stronger.