PinkPiranha makes a point I wished to say myself. I don't think that INTPs are particularly assertive. Assertiveness, to me, has always appeared to be an xxTJ trait, though particularly xNTJ, taking into consideration the fact that xSTJs are more likely to "soften" their assertiveness for sake of etiquette, or something along those lines.
xNTPs on the other hand, rather than being assertive, seem more blunt and oblivious to what might "upset" someone. I, for instance, am rather unassertive, but I am EXTREMELY blunt. I pay absolutely no attention whatsoever to social conventions, whether this be intentional or unintentional (occasionally a mix of both). I rarely realize how something I say could be perceived as even remotely unkind.
This is the problem I have with xxFJs, especially xSFJs. Whenever speaking with an FJ, I always notice how hesitant they are to directly say what is on their minds, or the truth, for the mere sake of hoping that nobody is "hurt." When this happens, I always pressure the FJ into saying the direct truth by insisting that I couldn't care less about the emotional consequences, I just want to know the truth. Still, they always seem to find ways to never directly state it. They always get very uncomfortable, and usually try to "fluff up" their statements, and try to avoid talking about the subject matter.
Similarly, even if they do not openly express it, whenever I say something considered to be socially unacceptable, I often can sense how horrified the FJs are. This, of course, applies not to all FJs. xNFJs can occasionally have their moments of "bluntness," however, the cause is, I think, different from the cause of bluntness in INTPs and ENTPs.
