(pinging some Tolkien experts who may know more)
That makes sense. What makes a bit more sense, perhaps is to realize that the Orcs are corruptions of life, not an original creation. Who is it who give a creature the will to live? Surely it is the same One who gives life in the first place. Twisting that gift of life to hideous ends - who knows what will become of the side issues.
So what I'm saying is that maybe it's not that Orcs hate their existance, though I am sure they do, but that Creation and all created being loathe Orcs and therefore the world is a far more inherently hostile place to an Orc than it is to a Human or an Elf. This is my Father's world; and He probably doesn't like people messing it up.