Lots of people seem to be jumping on the /thanosdidnothingwrong bandwagon, and I need some Catholic Church, Natural Law arguments to prove unequivocally that he did do something very wrong, even if the writers of the next Avengers movie never bother to articulate it in those terms.
Please respond to the following 5 objections:
Whether Thanos did anything wrong
When Thanos disintegrated half sentient beings in the Universe.
Objection 1 - It would seem that Thanos did nothing morally wrong in the course of Avengers Infinity War because all his actions were geared toward the greater good. His desired ends were merely the universal application of a successful method of societal reconfiguration. The mere platitude that it is never OK to do evil so that good may come about (aka the ends don't justify the means) is insufficient to explain the evil Thanos sought to wreak upon the universe. Generally when one considers ends, they are finite, not universal ends. Thanos' goal was a final good. One that wouldn't necessarily need to be repeated. After Thanos accomplished his goal, his desire was to "watch the sun set on a grateful universe".
when he dropped Gamora off the cliff to get the soul stone.
Objection 2 - Furthermore, what he did he clearly did out of love, as the universe showed him. He believes he sacrificed everything (i.e. Q: "what did it cost you?"; A: "Everything") to save the Universe - not unlike Our Blessed Lord.
When killing off entire worlds and populations and leaving half alive
Objection 3 - Others say that because his method was random, it was not eugenical. Eugenics is a morally reprehensible method of selecting which sentient lifeforms should live because the question whether one lives or dies is based on criteria that doesn't take into account the dignity of everyone's immortal soul; it only considers a person's worth.
When talking to young Gamora about his reasoning for his actions.
Objection 4 - The philosopher says "All things in Moderation", and Thanos woulds say that sounds "Perfectly Balanced". The universe was in trouble and needed a moderator to step in and save it.
When he killed Loki and Gamora
Objection 5 - Those who Thanos did kill, by himself and not randomly, and not as a part of his quest for balance, were killed out of self-defense or as a punishment for treason. Just war theory says that it is ethical to kill out of self-defense and it capital punishment is licit when it is necessary to preserve the moral order. Since his society of one would be harmed by those who ardently sought to assassinate him, he was justified in a those killings.