It's scientifically proven that bears can feel pain.
Pain is bad, all creatures instinctively avoid pain.
Humans can deduce that inflicting pain is bad (this is part of the golden rule and exists in all societies. Only sociopathic people fail to understand it, therefore it is a reasonable assertion to use.)
Humans must eat to survive
eating animals inflicts pain
Humans can either not eat animals, or inflict as little pain as possible to the animal.
Some humans pick the first choice, most go with the second. (Most hunters I know want to kill an animal cleanly so that the animal doesn't suffer.)
Bear dancing inflicts pain for entertainment.
Entertainment is not necessary for survival.
Pain is bad
Bear dancing is cruel.
Also, just because some people think it's not cruel, does it magically become okay. Some people think waterboarding isn't torture.