Why has the out of africa THEORY been presented as fact despite the growing evidence against it? Why have all other theories been so violently opposed?

Simple reason:

Its all about denying that we are different species. It is about denying that there is any significant evolution that has happened to us after we went our separate ways. It is about denying that force integrating us back together would lose any such differences. It is about denying the fact that we should not race mix. It is about justifying the genocide of the European species.

Basically, they want to selectively breed humanity, which they consider peons, into the dumbest and least capable species possible. They want to do this so that the we are not genetically capable of comprehending or resisting our enslavement they have us bound under. The easiest and fastest way to do this is to throw away humans and start with africans, who are already essentially as dumb and incapable of organizing as they want in their slave species.

This purposeful down breeding of humanity is protected from exposure when the lie of out of africa is taught, thus they fight diligently to keep up the illusion of us all being the same.