I don't understand animal rights activists

Animal rights activists want to kill this polar bear cub in the Berlin Zoo. When he was born his mom rejected him and his brother, his brother died but the zoo keepers were able to save him and keep him and incubator. Since then one of the zoo keepers has slept with him every evening to tend to his every need. Apparently that was cruel. Animal rights activists want Knut (the polar bear cub) put down, because they say life in captivity is cruel. Yes the animal rights activists want to kill the adorable animal. No they don't want to give him a snack or a new ball or even do some sort of hippytastic re-enactment of Free Willy, they want to kill the polar bear cub, who looks really happy, because apparently his soul is barren and empty on the inside for living in captivity. You know, I have some sympathy for animal rights activists when they are like "hey drilling holes in animals heads to see the effects of drilling holes in animals heads is not a good science guy idea!" But when the animal rights activists want healthy animal dead I take issue. Sort of afraid they will try and assassinate him as they are clearly crazy.