@Terry
The problem is leftists, centrists, moderate rights, far-rights, white supremacists etc. all mean slightly different things by "white replacement".
Some of these versions of "white replacement" are indeed racist conspiracy theories. Some are real effects that have been observed for a long time. Problem is, nobody is clear enough by what they mean by "white replacement" when they invoke it, so it all gets put in the same box with some really insane ramblings.