You do realize that by positing a need for “Nordics” to have no other ethnicities amongst themselves, you’re not showing much faith in their resilience–something I’d expect to be part and parcel of any sort of superiority–don’t you?
Seriously, look at, of all people, Nietzsche’s understanding of an übermensch–not bothered at all by “lesser” humans draining him because they can’t actually harm him. Just let them have their fun, don’t bother antagonizing them further, and move on.