Why would morally upright people be using souls and signing pacts with eldritch entities for personal power and advancement?

Ivy is nice but also a vigilante murderer, just that she murders bad people. The only actually good guy is Warden because he plans to Summon the Patron and immediately assassinate them while they're vulnerable from being newly summoned. And maybe Shiv actually, he's an asshole, but he's just a monster hunter, so, maybe he's a good enough guy? Then again, even Shiv and Ivy are willing to unleash an eldritch God upon the world in return for personal gain, so maybe actually the only actually good person who cares about the good of Mankind is Warden.