I think they cannot make that leap if they are reading at an emotional rather than intellectual level. Anyone, regardless of personality type, can think about something and understand others' rational arguments. If they react emotionally, it is much harder to do so.

The vitriol with which "Snapeophiles" are attacked personally is astounding. I see much less of the reverse, although it can occur. James/Sirius fans frequently react as Gryffindors - they make a quick judgment based on emotion and run with it. Right is right, and wrong is wrong, and never the twain shall meet.

Snape fans tend to be less volatile and react more intellectually. This does not mean that Snape fans are not emotionally attached to the character, just that I think they prefer to base their judgments on thought rather than feeling.