Well, this all started with him merging with the divine blood of a weaver goddess.
As for him acting like a human, I'd say it is him trying to hold onto his philosophical ideals. Even when he was a student, he argued for logic and understanding. He didn't accept warlords and their brute force approach. Would it be easier to kill all his enemies? I think even he'd agree it would, at least at the start.
This goes with his bet against the core daxia, where he came to this place to try to convince others to not join with the dragon slaying empire.
His brutality is focused on individuals, in hopes that others will not follow in their footsteps. A shinier weapon has yet to lose that battle against long term survival, and thus the series continues.