I think the key point there is that a cow magnet is large enough that it never gets past the rumen. Also, if a swallowed magnet hurt 0.1% of cows, but helped t

I think the key point there is that a cow magnet is large enough that it never gets past the rumen. Also, if a swallowed magnet hurt 0.1% of cows, but helped the rest because cows inadvertently eat lots of metal objects, then those 0.1% are seen as necessary collateral damage in the meat and dairy industry. On the other hand, if swallowed magnets hurt 0.1% (they don't, but bear with me) of kids, then it isn't seen as a necessary evil.