Each human race is represented by a different ET race that "created" them.
Many of the ET races are at war and have been forever.
The negative ET races want you destroyed because you are offspring of their enemy.
Any chance they get to weaken or destroy you they will take it.
If they can breed their children / descendants with yours, they will. This is a common war tactic. You breed them out of existence.
Do you wonder why they promote race mixing, but only do it to certain races while protecting other races from it?
Because the other races are their descendants they are trying to protect and keep pure.