Because at this point, there is a sharp divide between conservatives who care about fiscal responsibility and family values, and "conservatives" who care about unmasking (((conspirators))) in pizza restaurants. Although to be fair, the platform will likely attract nothing but the latter.
Actually that's not what I said it all. The concept on in/out-group can be completely arbitrary, e.g. assigned by flipping a coin. The principle still holds.
That said, since you bring it up, the history of humanity is largely the history of war between different ethnic groups. So yes, hating people based on ethnicity has been the norm for most of human history. It's still largely the case in varying degrees in different parts of the world.