The latter would argue that the former are violating the animal's right to a pain-free death.
Besides, most people have experienced a cut by a sharp edge where they don't feel pain or even realize they are bleeding for some time. This is actually a goal of Jewish and Halal butchering methods. And frankly, I'm not sure attempting to perform some 'pain-free' slaughter via impersonal machine is more humane than having another sentient being in close proximity to the animal perform the act. Modern factory slaughter is humane in the same sense a drone strike is humane.
So you really believe that every level of "feeling something" is the same?
And I kinda feel like the difference between factory farming and pasture farming probably has a larger suffering delta than industial slauighterhouses vs Jewish butchers. But for whatever reason people don't care all that much.
And while I can't say much about sheep, in the last ~50 years we have found that some kind of animals are remarkably far on the latter side