It's interesting, because I don't see any other types having a similar issue like this. NTJs and NFJs get along great (and usually prefer each other for romance). SFPs and STPs are fine, STJs and SFJs are fine, etc. But why would NTP and NFP turn out this way so commonly? Those other types *should* have similar issues, similar perception but judging it different. Yet the NPs are the only ones who conflict from it.
It really must be Ne. As you said, Fi with Ne assumes emotional implications. And that's because Ne is all about thinking out of context (while Se is thinking about the current context). And Fi would react to the NFPs perception of the implication, which when Ne is given room to wander, it will. And that's where the problem lies. With someone's blunt style, they will think that the person is trying to be hurtful. You know, all that jazz.
Yup!
What people don't get is that TPs and FPs can get together just fine, but ENTP + NFP doesn't usually work out as well as the others. So when ENTPs experience this, their immature Si and their Ne makes them assume that all FPs are going to be bad partners (just how I see it work out on here anyway). It's not Fi that causes problems, it's Ne. And it's really obviously that too. When NFPs and ENTPs talk about what they don't like about each other, they label it "Ti" or "Fi" and then start talking about NeTi or Fi + Ne.
You'd think that these hardcore rationalists would be able to notice that obvious fact.