Well when I say NEVER fold, I mean in this particular spot against this particular opponent... every spot is very dynamic based and you are right, your dynamic with him could be much different than mine. But here is the logical I am going with.
I am assuming that you look like a tighter, but capable reg to him. He probably does not think you are much of a spaz, I have never in my life thought that you were a 'spaz' by any times we have played if i'm not mistaken. I don't think that he thinks you're just going to spaz with QJ here or AJ or anything like that. You obviously certainly can though with the dynamic and it does make it a much trickier spot. From what I know about this opponent though, he is all about going for those mind-fuck spots where you get put on an insanely tough decision like this. Therefore, knowing how capable he is in these spots really leans this towards a call and reevaluate.
Also, you said what if a K smashes on the turn... That really shouldnt be a concern at all, if hes flatting like KJ here and smashes a K on the turn then you are just unlucky. I also don't think he has a flush draw with overs much by his small raise sizing (altho he's good/a weirdo so its not out of the question), so his range is really like overpairs or air and I think it's much more leaned towards air actually.
More likely, he will miss the turn and barrell again. I think the pot will be super inflated on the turn and you can see what kind of bet he puts out there. I think if he puts a bigger sized bet on the turn it's much more likely a bluff but like I said he is quite tricky so you never know.
Don't know how organized this rant of thoughts is lol but one last thing, it is super likely that he is 3-balling AA/KK pre imo... he 3-bets A TON normally so it just seems weird that he would flat here when you would prob gladly 4-bet ship 77 in his face a lot. Plus, I don't know how he is going to perceive your opening range from that early position, but he probably will think of it as tighter which makes gives more inclination to him 3-betting all his high pairs. I def don't think flatting is EVER out of the equation or anything like that, I really hate saying that I wouldn't ever do something in certain spots cuz that is frankly not true. I make some outrageous folds sometimes too based on dynamics, but you have to base it on a true dynamic and not level yourself. Guys like 'opponent' in this spot will constantly go after you in tough spots where you will 'level' yourself a lot about the dynamic and potentially make some tight laydowns for your trny life. I've played with opponent before deep in a $700 pca satty where the table was filled with easier opponents but he was constantly 3-betting me and getting involved in pots with me (not the normal strategy for a good reg at this table)... He does not play scared at all.
Hope that helps with the thought process there.