I frequently see reference to 'closed minded certitude' with reference to the INTJ type.
Well I can see the point, but like most things I don't think it's as simple as that.
If I were to say (forgive the UK-oriented example, but you'll get the drift) "Tony Blair was a superb politician, but a lousy national leader.", then a lot of people who disagree would take umbrage and call it closed minded certitude. If I were to say however "In my view there is a case for saying that whilst Blair was undoubtedly a superb politician, he did in many ways leave a lot to be desired as a national leader", probably fewer people would make the allegation about closed-mindedness etc.
In both cases of course exactly the same opinion is being expressed. But in the second case it is being clearly expressed as matter of opinion, leaving the door open to disagreement. Anyone who knows which end is up, would however knows that it is just an opinion, regardless of how it is couched-- how can it be anything else since it is merely a subjective judgment of Blair.
I have found that a lot of people are very sensitive to this, and react adversely to opinions being expressed in that way. Most INTJ's however probably feel most comfortable with that approach, and see little point in beating about the bush with apologies and solicitudes for their views. In fact they may well be expressing a view about which they are themselves less than certain, in order to stimulate an interesting debate.
Because INTJ's do a lot of thinking and evaluating, they are probably in fact less certain about many things than they appear to be. But their approach will often be, "That's the conclusion that I have come to on the facts and the evidence at my disposal. If you think I'm wrong then try to prove me wrong." They will be open to rational discussion, but too often the reaction to that is more concentrated on objecting to how they put over their point, than on sensibly and logically delivering a counter-argument.