I use spurs in place of a whip, because MY horse can't handle a whip. I would not be surprised if he'd been abused with one, considering what I'm told he used to put up with in his mouth.
Am I wrong? Maybe, but I'd much rather use a firm squeeze with a spur than compromise my position by performing what many call a "pony club" kick - legs out away from the horse's body and boot him as hard as you can in the guts. And yes, that is what it takes some days!
I think, like with any training aid, spurs can be used for many different purposes. Refining the leg aid is just one of these purposes. For as long as there have been spurs, there have been those who use them to reinforce the leg (classically the purpose of the whip) on horses that can't handle a whip, or will deliberately evade one by bulging out on the opposite shoulder, and so two must be used. I'd rather have two spurs than two whips! I might be exaggerating the length of time a little, but I know a large number of people who use their spurs for the same reason I use mine, and to great success.