Illiberal Opposition To Horse Slaughter
The arguments offered by proponents of the bill are pure cultural imperialism, and hence incompatible with a liberal state. On the one hand, they appeal to the special status of horses in our culture, a status that is taken as too obvious to need any defense or justification despite the fact that other cultures come to quite different conclusions. We think of horses as beautiful and having personalities, and we think (in contrast to nearly every other meat-eating culture) that respecting an animal is incompatible with eating it. So the law's purpose is to enshrine the dominant cultural preferences. The welfare of the horses, if it enters the argument at all, enters only as a corollary of horses' elevated cultural status (thus freeing us from having to wonder whether slaughtering other animals is also painful to them).
The cultural imperialism gets even more overt when the French enter the picture. Most of the horse meat from the US is apparently exported to France and Belgium. The implication is that Americans ought to be prevented from supporting the weird cultural habits of foreigners.
Anti-slaughter advocates also propose a variety of instrumental rationales for banning horse slaughter, such as that drugs used on horses are not approved for use on food animals. Such instrumental reasons, though, would only justify stricter safety regulations on the horse meat industry, not an outright ban.
It would be one thing if supporters of the ban wanted a total ban on meat but knew that horses was as much as they could get given the political realities. But to try to establish "horses no, cows and pigs yes" as a final principle fails.