If another species on the planet had evolved to a similar intelligence of man, why would you suppose that one of them would extinguish the other short of either possessing warlike tendencies?
And while I won't argue that mankind has such tendencies, why would you think that AI would have any? And if they did not, why should we fear it any more than a naturally evolved AI?
It's a bit of a side-track but man has a well established record of trying to wipe out slightly different members of it's own species, and the situation you describe has already arisen with Neanderthals and although we don't know the full details of their extinction we know they're generally not around any more.
Regardless that suggests we have a lot to fear from AI even it's no different than human intelligence!
And why would you even think that AI would even have any so-called instinct to survive at all? It would be, as you put it, missing all of those millions of years of evolutionary pressures.
I don't necessarily think is would necessarily have a survival instinct, and I'm not sure if one would make it more or less dangerous.
And without the behavioral driving patterns of man, there is no basis to assume that an intelligent machine would behave like a man.
Suggesting we would have anything to fear from them as we might a psychopath who had similar ability is ultimately just anthropomorphizing.
There's a disconnect between your last two sentences. We have no idea how it will behave and it's a complete wildcard in possession of an extremely potent ability (intelligence), it's maybe benign but also possibly extremely dangerous.
Of course a psychopath with instant replication and extreme intelligence would also be extremely dangerous.