The key point here is that orcs arise from human / elf cross-breeding, but have been banished to the forest as mutants.

There, the orcs live in peace and harmony with the natural world. They don't blame the wolf for eating the farmer's sheep. Why should they be considered evil for eating the same sheep.

They have developed a rich culture of lawful neutrality, which focuses on living in the moment. Quick to rise in temper, and quick to simmer down. They despise straight lines, and permanence (which generally don't exist in nature), and worship the boar-mother that ushered them into the world.

They resent both humans and elves, however, for rejecting them.