Do I really have to let my brother see our cat's mutilated corpse?
That is disgusting. Why do you want to keep your brother from seeing your dead pet?
Everyone knows he doesn't like our cat
Its the nice thing to do to keep your brother's mind safe from having to see something so horrid. Seeing a mutilated corpse like that could be very troubling to your brothers sanity, so its great that you are looking out for him.
It's not like he was close with our pet. I am just being considerate since he is not going to like it.
No matter your reason, it is good that you are protecting him even if it is not your intention. That is so nice of you.