The Question and Answer section for Divergent is a great resource to ask questions, find answers, and discuss the novel.
I think you must consider that Divergent is a dystopian novel meaning it is a profoundly flawed and unequal society. Stratified groups that kill each other would not make a good social balance.
What economic system are you referring to?
Tris feels angry and betrayed. Tris could expect something like this from Peter but was shocked by Al’s involvement. She could smell Al's hand and knew he was with Peter in the attack.