Disclaimer: the author is one of those liberal-minded academics interested in defending an oppressed people, sometimes to the disservice of their own objectivity.
Let's start with what the Freedom City book tells us about Deep Ones.
Deep Ones are Atlanteans corrupted by interbreeding with the Serpent People, as well as the influence of the Serpent Scepter.
What does it mean to be "corrupted by interbreeding"? When people talk that way about humans; we know what they mean, and we recoil from it. Deep Ones carry the blood of their Father Dagon and their Mother Hydra, the mighty gods that in the days of Lost Lemuria reached up from the depths Below and reshaped them in their image.
This is a shameful thing in our history books because the history books were written by the people who kept the ability to write; whose civilization weathered the great Cataclysm that destroyed Lost Lemuria
They have hairless, green, scaly skin, clawed hands and feet, entirely black eyes (with no iris or pupil visible), pointed ears, and sharp teeth. Their scales provide Deep Ones with some natural armor, and their eyes are adapted to see even in the blackest ocean depths, but they deal poorly with light as bright as daylight on the surface.
This is a common look for many Deep Ones, especially the ones that live down in the tropics or up along the eastern coast of North America - but the Children of Father Dagon and Mother Hydra wear the shape of their home waters. Arctic Deep Ones have the fat bodies of seals and move as slowly as a Greenland shark; riverine Deep Ones could almost pass for a green-skinned human. Not that there are many of the latter left. Their skins (labeled incorrectly) are in the British Museum - and in the Royal Museum in Atlantis (labeled correctly).
The ruins of Lemuria lie at the bottom of the Pacific, largely undisturbed, though occasionally visited by scavengers (human and otherwise) looking for ancient artifacts and secrets left behind by the Serpent Empire. Some scattered tribes of Deep Ones can be found there, usually worshipping some sunken idol or ruin.
When humans worship at long-neglected churches, or pray in shrines destroyed by fire, we admire their piety and their commitment to their faith. Why don't we do the same for the sons and daughters of Dagon and Hydra? The truth, as it ever is, is complicated.
Let's move now to legend and story.
Deep Ones eat people.
This has happened.
Deep Ones are endocannibalistic - they eat the bodies of their dead in homage to the maw of Dagon and Hydra, absorbing the power of those they've lost as a way of keeping their souls alive. A Deep One has never truly died if someone who has eaten their flesh lives; and so in some of the great cyclopean cities Below the chain of being goes on to the days of Lost Lemuria. (The Deep One word for Lemuria literally is Lost Lemuria in the dialect of Lemuria before the Fall.) Deep Ones are also exocannibalistic. They eat the bodies of fallen foes and feed them to their young; the better to honor a worthy enemy and to gain some of that power for themselves and for their kin. A Deep One might do things to the body of a Surfacer that would horrify said Surfacer but it's nothing they wouldn't want done for themselves in the same circumstances.
There is another reality to Deep Ones.
They are starving. They have been starving for a long time. Surfacer ships have drained their hunting grounds dry and pumped poisons in their waters; the pitiless mercy of Atlantis awaits if they venture out from the deep open oceans and rocky shoals where they have been forced by circumstance and centuries of unending warfare. If a tribe of Deep Ones should swarm a shipwreck or a crashed plane, hooting with a terrible cheerfulness as they bare their fangs, they are enemies to be defeated who will kill and eat what they can but they are doing it because they are out of food.
Deep Ones worship strange gods.
This is true.
Deep Ones worship their Dark Father Dagon and their Dark Mother Hydra (who have at times been worshipped by Canaanites and feared by Greeks) and believe that one day Dagon and Hydra will rise from the Depths and the world will be transformed. When the stars are right, the first will be last and the last will be first, the sea will be as the land and the land will be as the sea. The apocalypse will come and Deep Ones will rule where now they suffer. The faith of Dagon and Hydra is an apocalyptic faith that demands personal sacrifice and penitence; a Deep One with no tattoos, piercings, or other scars (in memory of the marks on Dagon and Hydra, left there in their long-gone wars with the foul gods of Atlantis) is no Deep One at all.
But their suffering - their suffering for faith, will be rewarded. The false gods of Atlantis will fall and Lemuria will rise, and there will be a new world. And perhaps this is cruel. But their faith believes in apocalypse because they need an apocalypse - an uncovering that will reveal the world for what it truly is. Where there will be justice for a people who consider themselves lost and hunted, where there will be a reckoning for a people who consider themselves to be sorely used. If they aspire to supernatural change, so have many fallen peoples down through the centuries. If they try to hasten the great day of Jubilee, as some do, so have many peoples over the centuries.
The difference is that when they do magic, it works. A charismatic priest or shaman will sometimes unite a tribe, or even a whole kingdom, for a raid on the Surface or against Atlantis - an attack blessed a thousand ways. The mingled blood of sacrifice will please Dagon and Hydra (for oh yes, I already said Deep Ones practice sacrifice and bloodletting, and mimic the great hungers of their gods through sacred cannibalism, didn't I?). The booty of the raid will feed a tribe, a kingdom, a people, until the time comes for the next attack. And if a warrior dies on said raid, their flesh will make a pleasing sacrifice for the tribe. It is a terrible thing to die on the land and have one's bones be buried in the dead earth.
Deep Ones love the water better than the air.
Yes. Yes, of course they do. Even for the more amphibious sort the light is always too bright here and the air has a killing dryness. Everything smells strange and the voices sound wrong, and everything looks bizarre. Their songs echo strangely in the air, proof of its disconnection from the realms of the gods below.
Deep Ones want to kill us all.
There have been Deep One invasions of the Surface - the most recent and most infamous saw an army of Deep Ones assault Freedom City during the Archevil Incident. Objectively they were cannon fodder and distraction for the Archevil's entity's larger plans for transcendence and global domination; but that hardly matters to the human beings they killed in the process. That was back in 2011, but you can find images and horrific accounts of their attack with just a little Googling. This is how people know what Deep Ones do - because they've seen it in action.
Sing a different song. When a nest of Deep Ones falls to an Atlantean reprisal, what do the Atlanteans do with the survivors? When a prisoner is taken after a raid on the Surface, what do the Surfacers do with her? That they are not as brutal as Deep Ones does not excuse brutality, nor does it return to life those who died in the cold dry ground Above or beneath the tridents of Atlanteans below. Deep Ones consider themselves in a war, and in a war you fight to win. There is nothing they would do to a Surfacer they wouldn't do to each other if suitably pressed.
What about the stories that Deep Ones have more than once subverted the Atlantean royal family; driving them to threaten the Surface in 2002 and actually invade it a decade and a half later? Well those stories are all true (and even now, there are agents in the Atlantean royal family waiting for another chance to strike!); but does the average Surfacer believe them? The Atlanteans would blame it on the Deep Ones, wouldn't they? One bit of supernatural subversion by the Serpent Scepter could happen to anyone but twice seems like carelessness.
Deep Ones hate Atlanteans.
Yes, yes they do, and the feeling is mutual. Deep Ones see Atlanteans as cruel, arrogant aristocrats whose goal is the extermination of their people. Atlanteans see Deep Ones as cold-blooded monsters whose goal is the extermination of their people. Both sides can point to atrocities, to killings, to tortures, across millennia of warfare, as proof that what they say is true.
Deep Ones resent Surfacers for their alliance with Atlanteans, for what they've done to Mother Hydra's oceans, and for the Deep Ones they've killed. They _loathe_ Atlanteans.
Deep Ones are sexual predators.
Why would they do that? That is nasty.
Deep Ones want to be my friend.
Deep Ones are obligate carnivores, raised from birth with the idea that Atlanteans are cruel and arrogant monsters and that Surfacers are callous, alien fiends. Through blood and sacrifice, they believe that the world will be reborn anew and the Deep Ones will be freed from the captivity that is their powerlessness. They are carnivores who can talk to their food and know it would prefer not to be eaten - but they must live anyway.
They will kill you because they are hungry and because stripping the flesh from your bones will be a sacred rite to them. They will kill you to send a message to their other enemies - to show the power of the sons and daughters of Dagon and Hydra over their foes. They will kill you at the command of their shamans, in the name of their dread gods, and of the coming apocalypse that will sweep away all the Surface world in waves of oceanic annihilation.
But they won't kill you because they are Deep Ones. They will kill you if they have a reason.
When they are monstrous, they are monstrous in our image. And that is the most frightening thing about them of all.
Edited by Avenger Assembled