Take my two atheist vegan friends for example. There is nothing in the Christian gospel that demands we do not kill other creatures to consume. But my atheist friends came to their own ethical conclusions from (very broadly) Utilitarian reasoning: I do not need meat to survive and be healthy, so eating meat is merely a pleasure to me. Animals suffer in meat production and slaughter, so I choose to relinquish the pleasure of meat in order to prevent contributing to the unnecessary suffering of creatures weaker than I in this world.

Subjective yes, but perfectly logical and acknowledging direct responsibility for personal choices and their consequences.