there is nothing wrong with defending your beliefs to the point where you are actually listening to the opposite side's arguments, and attempting to comprehend the argument being made against you. As long as you're open to the possibility that you might be wrong, everything is OK.
BUT when you're so entrenched in your beliefs that you grant no possibility of your error, we're in trouble. You've probably missed a great deal of this thread. Joshua has said at one point the idea of evolution caused the holocaust -- there is something wrong with that.  There have been a few times where he talks about having a good debate about the topic, but he's failed to realize that he's not playing fairly. It's not an open and honest game when one side does not acknowledge the validity of other side's evidence, and ignores the criticisms made against their own positions.
This is why it is totally fair to call him out on this. He has a fail-safe against any argument, that no one else enjoys... namely that any evidence presented that harms his view is merely the work of the devil, attempting to dissuade him from God.The result is that he has the ability to believe whatever he wants -- this sort of freedom is really dangerous to everyone. The rest of us are bound by the consequences of our actions, of our beliefs, knowing that we might be wrong. I simply point to the countless moments where religion has caused blood shed -- had the crusaders thought they might be wrong, the accusers of witches thought they might be wrong, those in a Jihad, the whole business in Israel, 16th century France, 30 years war in 17th century, ...this list really goes on for a while... If all of these people could have accepted the idea that they might not have it right, they would never have been able to justify the killing they did, or at the very least would have had to put their real motives out on the table for everyone to see.
Fundamentalism is dangerous, (some argue it's religious moderates who allow and defend the fundamentalists right to defending their beliefs that is the real danger  but that's a whole nother thread) and it deserves to be called out.
Mull this one over, it's a good summary of what i've just said:
 In the world, there will always be good people doing good things and evil people doing evil things, but for a good person to do evil --  that takes religion.