That's right. The Vampire Invite is a bug that is a feature which is only so clever because it was completely unintended. I can't imagine myself devising it, but we won't be getting rid of it so long as it doesn't get out of hand. But, I imagine abuse of the VI would quickly lead to the one doing the inviting getting themselves muted, which pushes things to whack-a-mole account creation, which is where everything else currently devolves to in a worst-case-scenario anyway.
"forbid vampire invites" would solve the problem immediately. That said, I'm not a fan of rolling out functionality that isn't currently necessary. It's much easier to develop site functionality for a site full of friends. A site full of enemies requires harsher restrictions. Problem being, you design a friend sight for enemies and it starts being more attractive to enemies.