Theory: What if Home isn't actually evil?
(Just a fan interpretation.)
If my previous theory about Ronald creating Welcome Home as a safe, structured world is anywhere close to the actual story, then I don't think Home is actually evil.
What if Home's purpose is to preserve the neighborhood exactly as Ronald Dorelaine created it: a safe, predictable place where everyone follows their role and nothing is ever "wrong"?
If that's the case, it would make sense that the black substance is coming from Home. Maybe it's not because Home is causing the decay at all. Maybe it's because Home is what's holding everything together after Ronald's disappearance, or because the neighborhood is simply getting older and beginning to break down.
That also makes Wally's behavior more interesting. If Home exists to preserve the rules, then Wally reaching out to the outside world would be breaking those rules. Maybe Home isn't trying to hurt him. Maybe it's just trying to keep the world functioning the only way it knows how.
