And some horses do have spur marks. In general barrel racing isn't abusive. The rider can make it abusive
I barrel race and I don't do anything abusive. I know some people pull too hard on the bit, but it depends on the rider.
Barrel Racing itself isn't abusive but some people who do barrel race abuse their horses though most don't.
It really can go either way depending on the owner. Personally I can only answer to myself, because I know how I race. I don't think the way I race is abusive.