I agree with the statements that INTPs wander into the same areas as a paranoid person would. However, I, as an INTP, would state that I am not paranoid. While I do not necessarily trust people, I do not naturally mistrust people either. Like many others, the thought "That woman has a long coat. Maybe she's carrying a concealed weapon." (note my subtle attempt to debunk gender stereotypes; recognize the general assumption about only men being dangerous, or at least more dangerous) This thought does not incite fear or mistrust of the person in question. If she had such a weapon, why would she use it? Why on ME? With those two skepticism, I lose most basis for any sort rational fear.
The problem inherent in the system described above is the eventual realization that it might be safer to, in the situation above, to avoid the person more so than I would had I not considered the possibility of him having a weapon. If there was ever a point for an INTP to become paranoid, I imagine it would be here.
In the last paragraph, I was left with a problem that I must confront. What is my rebuttal? My first attempt would be through the fact that the person need not be a malignant force in my environment; she may even be helpful. From here, I would use this possibility to negate the possibility of the woman harming me. With these two canceling out, I have no justification to either trust or mistrust the person and thus have no justification for paranoia. The potential flaw in this system is where the potential danger outweighs the potential benefits. (IE: woman could kill me vs. woman might make the general area safer; in this instance, the first situation is presumed to be negative much more than the second situation is positive) Without delving into how an individual would weigh the benefits, a rational (not paranoia driven) fear/aversion would be caused by the negatives outweighing the positives. This would further go on to state that, assuming one's weighing mechanism is flawless, that one would never be paranoid because of the justification behind their fears.
To ask to assume, however, would be too much. While one capable to accurately weigh a situation would not be paranoid, it conversely follows that if one could NOT a weigh a situation accurately, one could be paranoid. I cannot prove that I am not paranoid. I can merely offer evidence that I am in a state of lower paranoia due to my methodical search for truth. (which leads to an accurate situation-weighing mechanism)
As a final note, I will conclude that paranoia is a result of a distortion in either perception or judgment. All MBTI functions being oriented towards either, I propose a dysfunctional function in any type can lead to paranoia and that INTPs should not be singled out for being predisposed to this disorder.