My two dogs, Trooper Thorn and BeBop, have had to put up with being the Guinea pigs for everything I learned - and had to unlearn - about training. Once upon a time, I trained them with Cesar Milan-esque methods: light leash pops delivered at the exact moment that bad behavior started. This was usually no more than a furrowed brow or a stare as a precursor to bigger behavior, which the leash pop headed off. I also got into the habit of getting their attention when training basic obedience (sit, down) by giving them a light pop if they hesitated or let their attention wander.
Later on, after I learned positive reinforcement methods, I began training them in much more complicated behaviors - circling left or right, walking backwards, kneeling, crawling, fetching, etc.
Now, here's the odd thing: all those complicated behaviors? They respond to those with eagerness and verve. But "Sit" and "Down," the simplest behaviors? They do those very slowly and grudgingly.
Of course, it's not so odd after all. "Sit" and "Down" were paired with punishment - the leash pop they'd get when they were slow or let their attention wander. Is it any wonder that they're not eager to do something that so often made them uncomfortable? Yes, they'll do it, but they won't like it. The other behaviors were paired with rewards, treats for getting things right. Those behaviors they find fun and snap right to them.
I have decided to get off my butt and see if I can finally correct the damage I did with Sit and Down, if I can turn them into a more positive experience for my boys. But the truth is that I may never be able to get them to enjoy doing those fully.
And that right there is why you don't use punishment to train dogs - because the best you can hope for is grudging compliance. Punishment can make a dog obey, but it can never make it eager to perform, and isn't that what you really want?