Truly, what it means... in fact ALL it means, is that 12 out of 16 non-INXJs have answered that in their experience a majority of INTJs suffer from closed-minded certitude. Don't think that just because there are people who agree with you it makes you right, or that it makes your informal internet opinion poll amount to solid empirical data.
You seem to be saying, "12 non-INXJ people think we do, so therefore we must."
Ok, the majority of the people who answered your survey agree with you, but there are several reasons that might be. Could it be that's why they took the time to answer? Do you think that 12 out of 16 is truly a representative number of the population? Is it safe to say that if the majority of people think something is true then it is true?
Actually, this is all a bit academic, I'm not saying you're wrong about it, just that your argument seems to be based more on opinion than fact. Frankly, I think that perhaps the point is really a matter of opinion and cannot be argued about using facts, which is ok too. But please keep in mind that while you are certainly entitled to your opinion, I am not obligated to share it.