Now I'm genuinely curious how I would react. I think getting used to the smell of blood and viscera would be the biggest issue for most people. As to caring for others, I think most of us are way beyond that. We say we do, but we don't. We only genuinely care about a few people closest to us.
Still don't see what it has to do with maturity - it's just about getting used to it, like anything else. Bring a few more, play with some blood and guts, and he'll be ready in no time. Cut off some limbs along the way, so he can get used to screams of pain, etc. which will probably be way worse than deaths.
But since Ars can't even look at that, it's a good call.