Full Idea
The Barcan Formulas are a threat to 'actualism' in modal metaphysics, which seems regrettable since the Formulas are validated by standard modal logics, but clash with the plausible and attractive actualist view (that there are no merely possible things).
Gist of Idea
The Barcan Formulas are orthodox, but clash with the attractive Actualist view
Source
Ori Simchen (The Barcan Formula and Metaphysics [2013], §1)
Book Reference
-: 'Theoria' [-], p.1
A Reaction
He notes that the Barcan Formulas 'appear to require quantification over possibilia'. So are you prepared to accept the 'possible elephant in your kitchen'? Conceptually yes, but actually no, I would have thought. So possibilia are conceptual.