If they were truly good/evil they would have nothing to do with each other.
Not true. There are different aspects of being 'good'. Trust is a sign of being good. Hope is another.
Meanwhile, doing good to spite your father is, inherently, self destructive, selfish and undermines any nobility within the act.
If they were TRULY good/evil they would have existed on opposite sides of sanctuary living in peace but also purposely ignoring each other b/c they believed the other was either corrupt or too pure.
The Book of Cain says it took time for the demons/angels to co-mingle. They eventually reached some sort of equalibriem by being within proximity to one another. So in a sense they did corrupt/purify one another a little.
I'm not saying Imperius should like us I'm saying, especially after killing the Prime Evil (granted we released him) that humans, specifically Nephalem CAN be used for good. And he should also realized that he couldn't destroy us even if he wanted to because we destroyed someone who beat him with a stab and a roar.
Except Imperius could destroy us. Angels and demons have the power to do things Nephalem can't. If Imperius was given the thumbs up, he'd be able to effectively nuke all of Sanctuary, your character included, and wipe them from existance.
Nephalem are not inherently better than angels or demons in every, single regard. I somehow doubt, for instance, that your character would've been able to destroy the Diamond Gate just by shouting. Or open portals to Heaven/Hell. Or to summon up enough strength to throw a sword through a mountain sized diamond.
The only way a Nephalem can attain true power, power that surpasses Angels/Demons in every way, is by doing what Uldyssian did. Sacrifice themselves on a spiritual and physical, metaphysical level.
Just because we could best Diablo Prime doesn't mean we're invicible. It means that we can physically harm and damage the Prime Evil. We're not immune to their power and if Diablo stepped on us... we'd still squish like a pumpkin.
If Imperius walked up behind your character and shoved his spear up your butts, you'd be dead.