It's your story but I suggest you burrow deeper into the kernel of your concept , the key factor on which the entire story turns: genetic engineering, ergo, genetics.
Would it not be the case that genetic engineering is complicated, particularly engineering designed to manage something even more complicated than genes: human consciousness? And no production process is perfect. What are the chances of a rare production "flaw" that results in humans who start thinking for themselves -- hence, rebel.
Another possibility arises from the fact that genes are always evolving via mutation. What if your protagonist is the product of one of those mutations? A mutation that enables him upon reaching maturity to start thinking for himself?
(Either way, could not the flaw, a mutation also be how all the other rebels came to exist? Defective products who slipped through quality control?)
Seeing or hearing about the death of his boyhood friend is a great triggering event.. What if it triggers the "flaw" in his genetic code to start expressing itself? He starts questioning, having doubts, start thinking for himself?
Whatever, I sympathize with your task. A story in the sci-fi genre is a tough one to condense into a logline because it entails a world that only exists in your mind. Best wishes.