I do think a lot of times it can be more frustrating. With a fundamentalist it can be easy to write them off as delusional and beyond reach but with the liberally religious it is like seeing a glimmer of hope trying to break through but just unable to. It is as if you see a normal rational person going through great pains to try and disavow that rationality when confronted with the subject of religion.
When it comes down it though the really big issues are mostly the same. When someone accepts or rejects the idea of some creating entity present in the universe it follows with other statements that must continue to be true in order for that original statement to hold for them. When dealing with someone in the US that would normally mean that the idea of creator was revealed by Jesus. It would mean that Jesus died and was resurrected, and so on and so on. The original split is what leads to the irrational thinking more so than any other particular point.
I do disagree that they are the ones less likely to change their mind though, I think they are more likely it will just take time. It seems that when a fundamentalist Christian starts to move away from religion the process is fairly quick. It is as if once the illusion starts to fall apart it crumbles quickly. I have only talked with a few but it seems the transformation from a fundamentalist to a non-believer is a relatively quick one when it happens, rare as it may be. For the liberal religious the process is much more slow and painful.
The liberally religious will spend years trying to delude themselves to make their religion fit with their view of the world. They will attempt to twist truth and logic to make it coincide with their particular biblical interpretation. It’s not so much that they can’t understand reality but that they don’t want reality to be what it is, so they twist it all they can. For those people the whole process of stripping away belief is very slow because they’ve put in so much effort to make that belief coincide with the real world, it’s impossible for them to give it all up at once or to give it up quickly. Instead they are left to slowly peel away the layers, rejecting one small piece at a time until what they are left with hardly resembles the original religion at all or eventually ends up at the logical conclusion of disbelief. They can be reached though as long as those layers keep getting peeled away, you just have to give them time. Reality can be a scary place when it’s something you’re unaccustomed to.