What does evil even mean? Evil as defined by whom, because of what exactly? Good and evil are in reality subjective terms, and they have meant a whole lot of different things throughout history. It used to be that simply not worshipping the right god in the right way was a sign of blasphemy and thus evil. It still is like that in some parts of the world. Apostasy is punishable by death here and there.
If we're going to get this "real" in a gaming board discussion then we should probably not complete skate over what "evil" actually means. But this is usually done for expediency in any gaming context, because good just is, and so is evil. And that's okay, because playing a game usually means trying to work our way through a story rather than getting into the nitty-gritty of philosophy.
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Well I would encourage you not to conflate how our world works with how D&D works. In our world there are no Demons, Gods or Devils, or at least no empirical proof of them. We would classify evil as a mental health issue or unhealthy pathology.
However, if you read the PHB it does lay this stuff out. As has been mentioned, evil in D&D is a metaphysical force.
-The Hells are made of Evil.
-The creatures that inhabit them are made of that substance and so are actual evil.
-Evil seeks to perpetuate itself in D&D.
-Alignment dictates how that evil is expressed.
-Fiends gain power through corruption, subjugation and suffering they inflict on others.
As for "having tea with Orcs" as funny as that is this isn't a discussion about what actions we should or shouldn't take in the actual game. Orcs, whatever the underlying narrative and history are still a threat. But really anyone in the world can be a threat - depending. There are dangerous and selfish Gnomes and halflings. As a player you can deal with them however you see fit.