The average individual could not hold private gladiatorial contests, on a whim, at negligible cost. Killing a few innocents by torture, as public spectacle, is significantly less than repeatedly torturing large groups, as private entertainment, for as little as the average individual would have paid for their ticket to the cockfight.

Also, some people reckon the suffering of animals doesn't matter. They're wrong, but they wouldn't care about most of your examples (or at least they would claim it's because they increase the risk you'll do the same to humans, which is a whole different kettle of fish.)