harmful? negative self-talk keeps me going

Without putting you in my mind, it's stuff like "Quit being lazy, you can run your *kitten* a few minutes longer." "Don't you want to look like _______? Then you better not go over your calories. Step away from the refrigerator."

I don't see that as a problem, that is more tough love than negative. I say if it works and it is as harmless as that, go for it.

Agreed, particularly on the first example - but transition as you can to, "Look what you've done! You're controlling your appetite, making healthy food choices, and getting stronger!"
I started weight loss in a self-punishing, frustrated mode, but that only lasted about 12 hours. Then, after eating a Lean Cuisine meal, I thought, "I can't eat that sh**!", and decided I had to come up with a better plan for someone so basically deserving as I am. Goodbye, "Get your lardass up that hill!"