HE KILLED AN INNOCENT!!!!!!!
I knew Dexter will kill an innocent person in one of the episodes.
He killed an "innocent" last season (Prado's brother). What's the big deal? Granted I guess it was a defensive kill, but even still. One could say Prado was an innocent too, he wouldn't never became what he became if it wasn't for Dexter in the first place! One thing about Dexter, is that he seems to really F up the lives of a lot of people around him majorly (Doakes and Prado being the prime examples)...
It seemed that this past episode Harry was acting more as the Passenger. The real Harry would never have urged Dex to murder Trinity in the middle of the woods with no prep time or planning.
It seems to me that Harry obviously is the incarnate of Dexter's dark passenger. This is why suddenly Harry started showing up as present hallucinations instead of flashbacks (not to mention it's a very clever way of keeping the character in the show). But yes, of course Harry is the "dark passenger" now. He doesn't actually "exist" at this point...
I think Harry is just a representation of the Dark Passenger. The way he told Dexter to kill Trinity right there in the open was more like a primal urge rather than what Harry taught Dexter. Although last season finale had Dexter sharing some emotional moments with "Harry" so I guess he really is what Dexter thinks he would be.
This is a decent theory (the latter part of your statement) but I believe it's just Dexter's way of dealing with and sorting his thoughts. "Harry" has been helping him with clues in Dexter's finding, giving him advice, and on occassion (lately, anyways) seems to playing the negative aspect of Dexter's mind. Quite plainly, one could say Harry is both the little Devil and the little Angel upon Dexter's shoulders,constantly giving him input one way or the other.
and I forgot to quote it, but someone mentioned Trinity possibly having multiple personalities. I think this may be partially true. Most likely, he is a bi-polar manic schizophrenic. His moods seem to lean way in one direction or another, but never really a good mix of any moods. It definitely took a lot for him to not snap Dexter's neck during the ash scene, and he came back from that rather well, but I imagine that was more of a defensive mood so as to not blow his nice-guy cover too much. The guy clearly has emotional issues, and he may have been fighting a desire to get rid of Dexter in the woods last episode, hence the uncomfortable irritatibility.