I'm discussing the specific choice of what rhetoric they decide to use, not why they are using it. Why they are using it is fairly obvious at this point.
There are many different lines, arguments, whatever that could be employed, though. By paying attention to which ones are specifically chosen, you can learn more about their target audience, which is larger than simply fans of a white, ultra-nationalist ethno-state. Hence their need to continue to use rationalizations like this, instead of being forthright about their intentions.
This one in particular surprised me, as I didn't foresee it. They're usually more predictable than that.
This is sensible in the current social climate.