I've often lamented that I can speak eloquently when I am defending something to a person that is trying to challenge me, but it becomes much more difficult to speak freely when they are mild and ready to listen.
Don't be offended if an INTJ argues with you. It means you've interested them. Be offended when they go silent. It means that what you said is so inconsequential as to not even be worth the effort of picking it apart.
and this is why i got such mixed grades in school. it wasn't laziness -- it was boredom and disinterest most of the time. yet when something interesting was taught in an inspiring way, i got straight As.