This thread is putting a lot of horses before a lot of carts.
In the first place, essentially all primates believe that any other primate who is not related to them by blood should be killed, or at least driven away. Actually, this goes for most every animal they encounter, not just primates.
It is only when social groups arise that exceed the boundaries of blood relation (i.e., states) that this basic group survival instinct becomes (by necessity) repressed. The rub is that it is not repressed in favor of some set of beliefs that prohibit all killing of outsiders; rather, the favored "in-group" in simply expanded to include people that aren't related by blood. This is typically accomplished by introducing a religion that justifies living peacefully with all other adherents (blood relations or not) and also provides a tax base for a power structure to inforce this "morality." It is generally impossible to repress the basic urge to kill non-relatives without imposing some equally ruthless system in its place, since any potential replacement will have to contend with people who are willing to kill those not related to them, who must be either eliminated or deterred if the state is to persist. Which is to say that the result is increased destruction of outsiders; indeed, the greater economic gains that a state is able to make at the expense of outsiders relative to, say, a tribe, are exactly what provides them the necessary competitive advantages to displace said tribal structures.
This process can then be extended further, producing larger and larger in-groups tied together by increasingly tenuous connections, provided you manage to produce a succession of sufficiently powerful state/church institutions to sustain them. But you never reach a point where the whole dynamic is not sustained by the urge to do violence against outsiders, and if you ever ran out of outsiders, the system would collapse. So you end up with a world divided into states/nations/religions/civilizations that are fundamentally hostile to one another, all of which hold the belief that the rest should be eliminated in some way (this can become very abstract in advanced societies, but the basic element of chauvinism is always present).
All of which is to say that pretty much everyone thinks that those who are different from them should die, or at least disappear. That is essentially the definition of "people who are different from you," at least as "different" has been applied in this thread. Said another way, the decision not to want to kill some other group is indistinguishable from the decision that they are not "different" from you. The catch is that, absent some institutionalized power to enforce and sustain such a decision, it will inevitably succumb to the inherent hostility that all people feel towards anyone not directly related to them.
In short, the world has always been populated exclusively by societies that are fundamentally at odds with one another, and states and religions exist specifically to exploit and magnify such tendencies. Anyone who would pretend that any state/religion/civilization is somehow above this process is either a fool or a propagandist. It is not possible to believe in the superiority of your own in-group without also believing in the inferiority of all outsiders, nor is it possible to sustain such an in-group for any length of time without actualizing this propensity for externally-directed violence.