This discussion in a nutshell to me is (If I'm wrong, please clarify :P ):
INTP's are wrong, I can't prove them wrong but they're so stubborn they're not changing their opinion towards mine. They're stuck in their ways.
But that is just flawed on so many levels and I realize that can't be what you mean, but it looks like it. You seem to assume here that your opinion is the only right opinion.
You should be like: INTP's have a different opinion then I have. Well, they have theirs, I have mine. We can consider each others opinions and maybe reach a consensus or we can not.
It's not a question of being rigid. It's a question of being realistic.
edit: For clarification.