Probable Muppet wrote:

the thing that really doesn't make much sense at first is that at the beginning of the movie Harrison ford is forced into commission due to him supposedly being the best man for the job and then he literally bumbles through the whole movie and gets his ass kicked in almost every scene. His role only makes sense later when you realize that he himself is a replicant.

I don't think he needs to be a replicant in order to explain why he got the job. He could have been human and the best man they have, but since he's up against the best replicants ever created that necessarily means he's going to get his ass handed to him. Anybody else might have fared much worse. And don't forget that he doesn't really want to do the job and drinks throughout the whole movie.

Probable Muppet wrote:

I think most people can identify with even the "bad guys" or the replicants that he is hunting. There are no bad guys in the movie besides maybe Tyrell and the Tyrell Corporation. One of the biggest themes of the movie is the question of what it means to be human and when you realize that Harrison Ford's Character might be a replicant that just brings that question up in a more interesting light.

When I first watched the movie, I didn't realize Deckard could be a replicant and the person that I found most interesting and had the most empathy for was in fact Roy. When I rewatched it, thinking of Deckard as a replicant, I became more sympathetic towards him, because now he was just as much of a victim as the ones he is hunting.

I think both readings of the movie are equally interesting. You don't need him to be one or the other. This isn't a normal action movie were you are rooting for the hero to win and kill the bad guys. You don't need to identify with any of the characters on the plot level. They are all thinking beings confronted with their own mortality whether they're human or not. That's enough for me to identify with them.