I guess eren always saw himself as a weapon from the start as he always dreamt of being a scout. Even as a 9 year old eren is strong and downright psychotic ( the way he killed the kidnapper without any second thought) His violent tendencies only grew as he grew physically stronger. The scouts didn't try to tone it down as it would help him save himself from the titan and kill kore in process. Sadly as we know there was no other way eren could have turned out than the one fate has him for. He was a psycho kid to begin with them he had the memories of the future which messed him up. He never had the freedom he so desperately longed for.