Harpies and vampires in the spirit world?

Spirits sometimes have to fight to keep the harpies and vampires away from those they love because their people are so ignorant they allow themselves to drift below the boundary line where they always conquer. 

They must be very, very strong in spirit to be able to vanquish the low when they are on our plane. 

They must have been here long, and have wiped from their own hearts all lower qualities not to risk being at least crippled by a band of the strong lower souls. Were they high enough to easily conquer them they should then be unable to connect with us. 

See how it works? 

Those who remain on the border are subject to the ills this plane has. 

—Helen in Spirit