Because it isn't projected. It's woven into our being. Value each other defined how? Value each other compared to what? If you're someone who doesn't believe in human life having intrinsic value (as distinguished from plant life, animal life, etc), then you can still choose to place value on human life of your own volition, but you have no logical basis for it other than that it makes you feel good. The problem comes when someone "feels good" by devaluing human life, by treating people horribly, hurting them, murdering them, etc. And if they devalue human life, you can't tell them they're wrong unless that value is actually objective. Otherwise they can just say "f*** you and your idea of value", and you'll have no logical foundation to say they're wrong.