Ah, plot holes. Suspension of disbelief only goes so far. Taken past that, the band snaps loose and you get hurled out of the work of fiction and right back into reality, immediately and forcefully. Bam. Immersion lost.
See also: Seeing a movie that has a huge plot twist, then replaying the movie from the beginning (even if in your head) with that twist in mind to see if the movie actually makes any sense at all.
Speculation can be fun -- What could be done with this story, or with this character, scene, piece-part, etc. ? Often, though, the author's messed his own fictional world up too much for me to care. If he can't get his straight, then there are plenty of other, more fulfilling universes out there for me to dabble in.