I’m a very shy INTJ. I can give you my input, but I am not him. If you really want him to be more chatty, it may be a good idea to ask him about this.
First, please don’t tell him why he just doesn’t “act natural”. Despite what may be natural for you, it’s apparently not natural for him. It feels like a putdown, it’s a reminder of how much he doesn’t fit in. It’s like if I was to go to a class of Pre-Algebra kids, give them a Calculus problem and then ask them “This is so simple! Why can’t you solve this?”
Second, does he seem to take a backseat in all conversations? Or only ones about those “serious” issues like religion and politics?
Unless I’m chatting with just 1 person, I always take a passive role in conversations. It’s hard to get a word in edgewise, when the chattier/extroverted people just keep talking, and I find it extremely rude to interrupt. So I wait until somebody actively includes me in the conversation.
In regards to the political discussions, I avoid talking about them for 3 reasons.
1) Everyone has gotten swept up into all of this emotional advertising, and ignores logic.—Given that your friend is an INTJ, and you mentioned he doesn’t fall into trends, he probably doesn’t fall for the emotional advertising either.—My facts and logical arguments go in one ear and out the other, while they fall in love with posters calling Obama an islamofascist socialist, with a little Hitler mustache drawn on him. And I just don’t feel like there’s any reason in using reason on the unreasonable. Sorry, I couldn’t help myself.
2) I don’t want to hear a point of view that doesn’t have its facts to back it up. So, in turn, I don’t ever want to give my point of view, unless I have the facts to back it up. I don’t ever want to encounter a part of the conversation where I’m not 100% certain in my answer. This is where I worry about people laughing at me (either out loud, or in their heads). So if I’m not completely certain, I’ll just avoid it.
3) I just don’t get the feeling that people are actually interested in my opinions in the first place. But that may just be my insecurity speaking.
So, what can you do to help get him more into the conversations?
-Try to actively include him. Ask him “Hey, what do you think about XYZ?” That way he knows his opinion is wanted, and he knows it’s his opportunity to speak.
-Try getting him more chatty in smaller groups. You say he’s open to chat when he’s with just you, but he clams up in big groups. What about when it’s you two plus one other person? Or two other people? with fewer people, there’s fewer people to laugh at him, and fewer people to interrupt him.
-Try to warm him up to the conversation by talking about things that he does know about and is interested in.
I commend you in your efforts to get your INTJ friend out of his shell. Just don’t try to push him too hard.