Well I feel like the bad guy is technically the King who is making the hero party defeat the demon lord. From we have seen the demon lord doesn’t have any malicious intents to enslave the humans or take over their land. But in the point of humanity, yes he is the “bad” guy
There are no sides. Neither is good nor bad. As they said, the heroes job is more as an entertainer than anything else in this time but since humanity views humans as the heroes it has caused people to look down on demihumans and other races, causing discrimination and oppression. MC is now going to fight against the view that "monsters" are bad guys and defeat the "heroes" to give the non-human races hope again.
MC becomes the bad guy??