Isn’t it possible to preserve the minhag of kaparos with chickens but not be oiver on tzaar baal chaim?
Yes of course it is. Like my local (London) minhag kaporos centre, where they are transported in the same manner as all fowl (x number of chickens per crate) in the early evening, each one taken out, shlugged, and put into another crate where they are loaded onto a truck and taken to the shachthois.
I don’t see anything in that 1-2 hour excursion that is tzaar bar lchaim and indeed the local animal rights people couldn’t find fault!
I strongly suspect that most of those protesting are just embarrassed about this minhag yisroel torah. Otherwise, they’d speak about bringing takonos and easing regulation to ensure those sites that mistreat or waste chickens change their ways.
Instead they invent new arguments each year, much like the anti-shechita groups, not to reform or better things, but to abolish and mock.