I'm confuzzled by the viewpoint that some of the above bits are cruel, yet it's OK to use a noseband if your horse is avoiding the bit.
What, so he can't get away from the pain of it and has to grimace and bear it? No. If the horse is fighting the bit, the key is not to tie his mouth shut and force him to submit, but rather to change to a bit he likes and/or correct the necessary holes in the training. I've been saying this forever, but recently saw the following posted on the Myler Facebook page:
Nosebands can make a horse's head look more elegant by breaking up the length of the head; if you must use a noseband, adjust it loosely. Don't strap your horse's mouth shut over the bit. If your horse is opening his mouth over the bit, there's a reason for it. A snug noseband can also cause painful lesions as the cheek is forced against the upper row of teeth.
Press your hands against your cheeks and move your lower jaw up and down. We had the opportunity to meet a terrific equine dentist at the CHA conference last October. She explained the lesions--she's seen them frequently but they aren't really noticeable with just a cursory exam and a standard float. It was a little startling to learn what goes on in a horse's mouth. I'll post her name when I find it. She was an excellent speaker.
As for neck-reining / curb, to me, it depends on the curb bit. A solid curb should only be used on a neck-reined horse. A broken curb, however, can be used with direct-reining, and frequently is. If it's a good, well-made bit, designed for this sort of use, I personally would have no problem using it on a horse that did not know how to neck-rein. I'm not sure that I would use that bit to introduce
the concept of neck-reining to the horse, however.