They probably understand others have different values. The confusion is, some values seem so self evident that its bewildering anyone with a certain level of intelligence wouldn't realize the same values.

I think the answer might be that they do have the same values, but they have a different model of the world overall, which calls for different ways of achieving those values.

To take this to an extreme, imagine a person fighting for their life against actual criminals threatening vs a person fighting for their life against a random person they think is a shape-shifting alien impostor. Both are internally justified by the same values, one is externally justified by a more correct perception of reality.