The word hate can be defined in two ways. The first meaning will term hate as an intense feeling of dislike and aversion. Meaning the individual dislike towards anything to the point of avoidance. While the second will mean passionate dislike and feeling of enemity. Hence, I'll like to state that there's two types of hate. I call them the minor and major hate drawing from the standard meaning of hate as stated earlier.
A minor hate is one possessive character or behavior towards something, someone, an object or anything else as long as the word hate implies. This is the type of hate everyone exhibits now and then, it's sort of a harmful hate or dislike to be precise. "I hate dirt and dirty people".. This is a typical example of a minor hate statement or behavior which is generally common amongst all people.
A major hate on the other hand is what drives humans apart. Am sure this the type of hate you had in mind when you came about this question. This type of hate as defined in the word is the passionate dislike towards a particular groups of people. Now, am not sure how some people come about such hate, I can maybe relate it to personal grudges, nurturing and probably psychological state of mind. But am sure about this type of hate is that it has the driving force to compel violent behaviors, as far as murder towards the hate target.
If you take away religion, race, cultures, and some other forms of geo-political groups formation, maybe the world would have less major hate towards one and another because those are the factors that sets humans apart. If maybe the while world was one big region without diversity, we probably won't be experiencing so much hate as we see today.