In Crisis Core, the wear, tear, and rust on the Buster Sword symbolized Angeal's tarnished honor; it also reflected that he couldn't care about maintaining the sword, and the more scars it had, maybe the less he dared to face it, and perhaps the more pain and bitterness were plaguing his heart.
From carrying it on his back as a good-luck charm and rarely using it, to being unable to carry it on his back, putting it down, and using it before the final fight, Angeal’s changing attitude towards his most important and cherished thing is a silent yet visible account. The very growth of his wing made it impossible for him to carry the sword on his back, just like monster and honor were inherently incompatible within him, and this might be one of the first and direct physical facts that pierced him.
After stepping into the vat dyeing of Shinra’s political propaganda, invasion and so on, was Angeal’s dream and honor instilled by the external environment, or self-construal, or the combination of both? In any case, while he gave lectures of dream and honor in Shinra, his belief might be effectively absorbed and utilized as part of Shinra’s military propaganda and education, with him being recognized as the spiritual leader of SOLDIER. But as for the question of its root, I tend to think that it was nurtured by his parents' upbringing, at least at the beginning, and Angeal internalized it with a strong sense of personal identity.
His dream and honor might align with and might be influenced by Shinra-brand military propaganda. However, I do believe that it was essentially derived from a core of his own, which he insisted unwaveringly, and had its root in his upbringing. And when he told Zack on the highway, “Our enemy is all that creates suffering”, it could be seen as a reconstruction of his SOLDIER dream after being shattered - a change arose within himself, originating from the breeze of Banora, rather unrelated to Shinra's military propaganda, and served as his new purpose. Yet, this dream was not enough to stand as a pillar to support his life: it was essentially unrealistic. Despite being a 1st, he (along with Zack) stood little chance to defy the huge Shinra political and economic system. For Angeal, this dream would ultimately remain unfulfilled, passing down from generation to generation, with the specific target slowly shifting from Shinra to Sephiroth. It was also because he made his own suffering - he was the enemy of himself, what he insisted firmly turned into thorns entangling him. Maybe it was because of the feeling that this self-tearing torment would continue until death might bring an end, he chose his own death. The last monster he killed was himself.