I’m not a PETA fan, but euthanizing animals in shelters is standard practice in the vast majority of animal shelters. There’s a movement, known as no-kill shelters, in which they only “put down” those who are aggressive and dangerous or already dying. But they’ve only succeeded in taking over a small slice of the animal shelter world so far.
Some authorities permit causing extra pain to animals in order to make more money (which is what the various animal welfare abuses in modern factory farms are for.) Other authorities disagree.
It is better to be strict and only buy meat and dairy and eggs from producers who don’t engage in the cruel practices common in the modern industrialized factor farms (like beak-cutting, confining animals in small spaces, etc.)
Our ancestors only ate dairy and eggs and meat from small producers — there were no massive factory farms in the shtetl! Everything was cage-free and grass fed! Factory farms inflict a lot of suffering on animals that we know from experience is not necessary, and these particular techniques are not part of our mesorah. So why get involved in it? To save a bit of money or afford more meat and dairy and eggs? It’s not worth it.
It’s true that some of our ancestors force fed geese, but at that time pate was believed to be an important health food that could provide necessary nutrients. And modern poskim have all banned the practice. Similarly cruel practices such as those involved in veal raising have been banned by Rav Moshe.
We should also work toward legislation, along with non-extremist animal welfare groups, to reduce the worst practices to reduce unnecessary animal suffering.