Actually, I think Deckard being a replicant makes the movie a lot more interesting.
Basically, the movie start with a dark world and a typical "human:good / machines:bad" point of view. Then, we realize it's more complicated than that and our minds begins to open up. When at the end of the movie we realize that Deckard may also be a replicant, it's the final step toward opening up our minds. It forces us to think back at the movie and view characters beyond stereotypes. It makes the plot more intricate. More importantly, it leaves us with a strong feeling that there's more than meet the eyes.
Of course, I understand not everyone like intricate plots, I understand not everyone like to stir up their preconceived ideas, I understand some people prefer simple pop corn movies, but that's certainly not my case!
Anyway, beyond my personal taste with movies, I believe you are irrational. It is Ridley Scott's movie. No he did not write the script, but a script is just a tool used by the director. Once the script is written, the writer is out of the loop. The end result is at the mercy of the director who can do whatever he wants with the script. There are plenty examples of writers who were pissed because of directors creating a completely different movies than what they envisioned with their scripts.
You said it is widely believed Scott made that comment to stir up controversy? No it's not. Not only it is not "widely believed", but it certainly was not to stir up controversy, it was on the contrary to end discussions among fans and clear up things.
Firstly, let's be honest, it's not a "controversy" at all. I mean if Scott would have said that Deckard was human, like most people I wouldn't care much. I do think the story has more depth with Deckard being a replicant, but it's not like it will change my life or anything. I like to think about ambiguous ideas, it's a fun game, but when the author decide to clear up things, I believe it's completely ridiculous to contradict him.
Secondly, I remember an interview with Ford stating he had an argument with Scott saying it would be better for Deckard to be human so spectators could identify themselves with the character. From what I gathered, Scott wasn't sure about Deckard when shooting, he tried to leave his options open, it's only when making the cut he decided it would be better to make Deckard a replicant. So the idea that it was just to "stir up controversy" is simply ridiculous.
Anyway, my question was not about your "arguments" nor the movie. Deckard is a replicant, we now know it, end of story. My question is about you. I'm simply curious as to why it is so important for you for Deckard to be human. Why you are willing to even deny what the author of the movie is saying. Even if you prefer more stereotypical stories and so don't like the implication of Deckard being a replicant, it's just a movie! So why the passion? I just don't get it!