The claim is that some amount of animal cruelty is justified because suffering is a part of life because, to know what joy is, suffering is just an integral component.
Let's assume that you treat animals very, very well right up until the day they are slaughtered. Then how can it be "learning" if it's their last thing on earth? So if it isn't learning for the animal, then what - is it a lesson for the slaughterer? If you're killing something so that you "better understand joy" that would seem to be "killing for your entertainment" by just some other name.
Any action ever can be justified as being part of the unethical suffering that helps someone understand what the lack of that suffering means. "Hey man, I just stole your car so that we now all appreciate not getting your car stolen". This is not a great defense.