Pippin's shock and outrage throws Bellamy off for a moment. In fact, it throws him more than a little off. He knew that Earth borns were prone to getting angry, same as the ones that were born on the Ark. Only difference was that the Earth borns and those on the Ark could survive in different climates.
"Ranging from 17 - 23." It's said as if it didn't mean anything to him. Which wasn't entirely true, it did. He'd only ended up going because his sister was on that drop ship. No one else mattered to him. "A society that was dying anyway," he counters when she asks what kind of society did a thing like that.
He shakes his head," I'd agree with that if I didn't have a little sister somewhere out there." A sister who had been his responsibility his whole life. Whom he'd named. Who he had practically raised.