Ethics protests aren't so enshrined for one. The views of ethics are often personal and ideologically entangled to some degree. Self selection has been more favored and the protests bring to mind the "obvious" but assailable objection "Why not just quit and associate with others more like-minded." It gets into messy areas of rights of association in ideal vs practice. Ideology isn't protected and is explicitly trumped by other areas like anti-discrimination laws.
Many can see "strawman" can of worms being opened (they may be reasonable in this case but what of successors) accepted as a norm without a sensible defined law or doctrine. There were the whole clerks refusing shall issue marriage licenses and nobody wants a situation disrupted by free rider "do nothing vegans in the slaughterhouse" or similar absurdities.
This isn't saying the current situation is ideal at all but that changes are non-trivial and there are reasons to suspect the precedent would be preferrable to most.