The original reason for Adam's rage was Magnus's experiments and the fact that there were children, mostly girls, in the pods.
Adam couldn't imagine what Magnus had to say to keep him from killing him on the spot, but... Magnus had managed to shock him.
It wasn't surprising, though, since Adam couldn't have known about the existence of hybrids.
After all, Nessa was the only one and it was unknown whether other hybrids like her would ever appear. As long as there were none besides her, she wasn't a separate species but simply an anomaly for which there was simply no explanation yet.
"As I said at the beginning, some of these children are here of their own free will, and some I took away when they were near death. You should know better than most that it's easy to get hurt in the slums, too easy, especially by children that don't yet understand the cruelty of our world." Magnus said calmly, glancing at the pods.