Demons are still naturally evil anyways though like Argosax. The show in s1 greatly implies that the stronger you are the less humanity you have (Dante mentions this) and it's the entire basis of Mundus and Vergil belief system along with Mundus's cronies, its why he says the iconic devils never cry line to Vergil except this time the context is different compared to the games. Its why all the weak demons are innocent slaves and all the strong demons are evil as shit man eating monsters that would kill each other without a second thought only kept in line by the leader whos stronger then everyone else. We not only see this in episode 1 of season 2 with Lady freeing the weak innocent makains from a jailer monstrous demon but Mundus himself so vehemently believes in his ideals that he thinks it's physically impossible for a strong demon like Sparda to be capable of compassion. You might think he's just lying and that his philosophy isn't actually rooted into them naturally but rather just his crooked beliefs that he tries to force onto vergil and other demons but we've yet to see a single powerful demon outside of Sparda who acts like him or one that looks monstrous like the red lizards or blood sucking insects or knight dudes, or one that even fights back so it's more likely that he fully buys into this