I feel like maybe somewhere along the way, some folks have lost the meaning of these words...
unethical
[uhn-eth-i-kuh l]
adjective
lacking moral principles; unwilling to adhere to proper rules of conduct.
not in accord with the standards of a profession:
She treated patients outside the area of her training, and the appropriate medical organization punished her unethical behavior.
humane
[hyoo-meyn or, often, yoo-]
adjective
characterized by tenderness, compassion, and sympathy for people and animals, especially for the suffering or distressed:
humane treatment of prisoners.
acting in a manner that causes the least harm to people or animals:
humane trapping of stray pets.
Is using a 50bmg humane? Is it capable of delivering a consistent, quick kill? Then yes. It’s humane.
Is using a 50bmg ethical? Well, one of the tenets of hunters is to waste as little meat as possible. As was discussed above several times, shot placement is the key to this - no matter what cartridge you’re using. So yes. It’s ethical.