Moral panic

Transphobes are stuck on the "usurping womanhood" argument because it is by far their best line of attack. By using the scare tactic of usurping and replacing biological females they more firmly emphasize their moral panic and sell it to the public. 

The problem for them is that the majority of transgender people are well versed in biology and all the argumentation around it. They don't for a moment argue against it much to the chagrin of criticals.

If transphobes drop the usurping argument they are left with simply allowing transgender people to exist in peace which is a non-starter. Therefore, they can't ditch the line of attack of replacement theory sparked by social contagion. 

I can only come to two possible conclusions here: a deep level of stupidity or willful malice.

Pick one.