That's the same trick used on the great replacement. Pick the most conspiratorial, unlikely version of it (evil Jews meeting in secret, plotting to cause immigration to turn whites into an oppressed minority in their own lands, and for no other reason), show that there is no evidence of that, the apply the label of "debunked" to anything that can be vaguely called replacement (relative demographic reduction of white population due to immigration policies enacted since the 1960s).

In other words, an offensive motte and bailey strategy. Attack the motte, then claim you've destroyed the bailey.