I agree - your Negative Voice CAN be a good thing. I wouldn't dream of dismissing mine just because it's at odds with my positive intentions, since it's usually trying to point out a legitimate obstacle that's either going to slow down my progress or stop me in my tracks entirely if I don't take notice and remove it. To give an extremely basic example, I could tell myself that I'm going to lose seven pounds by the end of the month. "You'll never do it!", my Negative Voice might say.
"And why not?"
"You'll feel too much of a failure after single-handedly polishing off the industrial-sized gateau you've somehow managed to cram into the fridge, and then you'll end up comforting yourself over your failure with the carrier bag of chocolate bars you've got stashed under the bed"
"Quite right too, Negative Voice, I hadn't thought of that. I'll just pop next door now and give the lot away to one of the neighbours. You can just clear off - I shan't be needing YOU any more!"