I don't feel the need to trust your quotes (...the bolded parts) as true identification of an INTP. I especially do not like the "They're very tolerant and flexible in most situations, unless one of their firmly held beliefs have been violated or challenged, in which case they may take a very rigid stance" ...Why do they simply state that a person's "beliefs" have to be challenged? Anyone will take a rigid stance if someone doubts their religion. Those who are Type 2 (enneagram) will take a rigid stance if the think someone doesn't know how to go about helping themselves and type 2
"correlates" with Fe. I think any one of the MBTI types can take a rigid stance against anything, but the four judging functions will do so in different ways. In what ways? I don't know right now. I have to think about it.
But anyway, maybe you're right. I really do have to think about it more.
Gah, I wish they had a whole college course dedicated to studying Jung's work, though. I do much better with a textbook xD