Sacrifice one life to save many
Utilitarianism vs Value of the individual
That’s the philosophical conflict in Infinity War.
Thanos believes that species naturally bring themselves to extinction and killing half of a population is the only way to prevent such an extinction. He is ultimately utilitarian. He believes that some lives should be sacrificed so that more can survive.
The opposing philosophy (value of the individual) is best expressed by Captain America:
“We don’t trade lives.”
He believes that sacrificing someone (innocent) is wrong even if it has the possibility of saving many more.
This movie is exceptional. The action is great, and the plot moves so fast, but we never lose the sight of the goal. And almost every scene has a character making a choice relevant to the conflict.