The trouble with saying that competition creates or is the cause for abuse and cruelty is that it leads to good, compassionate people not wanting to compete. Which then leaves the floor open for those who will do anything to win. And because there aren't enough people who acheive the top results through good training, the people who take the abusive short cuts keep winning, which makes even more good people want to quit competing, or leads them into more and more abusive practices to try to keep up.
If we had more people going in to competition, with a reputation for good, fair training and lots of hard work and winning, the prevalence of abuse would reduce, simply because newcomers would see that there is another option. Granted your always going to have those who want a quick fix, but hopefully with better role models around, there wouldn't be so much pressure to move to less than desirable training practices.
That said, if certain results can only be achieved through those abusive practices, and those results are rewarded in the ring by the judges, thats when things have really gone overboard. The example that comes to mind is the movement of those "Big Lick" type shows. If that exaggerated movement can't be achieved through breeding and training alone, then it should be penalized by judges, not rewarded. *Disclaimer, I don't know much about the Big Lick world, so if I'm wrong, please excuse me.*
I ride primarily Dressage. There are abusive practices in the Dressage arena, particularly higher up. But the presence of those practices is not going to make me quit training and working my horse in a fair manner, nor to stop showing. I will take my mare as far as we are capable of going while maintaining my principles and considering her and my abilities.