If I got a euro every time someone in history has justified invasive medical procedures on non-consenting creatures or individuals by saying it’s harmless and painless… well I wouldn’t be rich, but I’d still have an interesting collection to show my guests…
Putting a microchip in them like is done with domestic cats works just as well to have a quick way of verifying if a trapped cat has already undergone neutering, and at least it’s not mutilation. Coincidentally, that’s the standard procedure for TNR here in France…
it's just the tip of the ear, it's done
under anaesthesia, they don't even know it happens, and it heals very easily. much less expensive than a microchip, which means more cats can be tnr'd, and cats will not even have to be approached before being captured (unless they have distance microchip scanners?). not that a microchip is a bad idea, just that ear tipping is much more accessible.
it's not really any more monstrous or mutilating than capturing and neutering them (or microchipping them for that matter). they're not cutting part of their tail off or pulling their teeth out, it's a procedure intentionally designed to not harm the cat, but make their neuter status easily identifiable. they will not feel their ear getting clipped because they will be anaesthetised, it's very unlikely to have any complications, and it will have zero lasting effects on the cat because it's such a small piece of the ear.
i really, really love cats and if there was any evidence that eartipping caused lasting harm to them in any way then i would be in total agreement with you. but considering how easily eartipping heals, how it doesn't cause lasting pain or damage, how it lets cats be identified as neutered at a significant distance without having to even approach them and cause stress, how accessible it is, and how the cats are already undergoing an invasive procedure regardless, i don't think eartipping is bad or inhumane.
i think this is massively a cultural difference, though