Full Idea
In temporal logic, if the converse Barcan formula holds then nothing goes out of existence, and the direct Barcan formula holds if nothing ever comes into existence. These results highlight the intuitive absurdity of the Barcan formulas.
Gist of Idea
The temporal Barcan formulas fix what exists, which seems absurd
Source
John P. Burgess (Philosophical Logic [2009], 2.9)
Book Reference
Burgess,John P.: 'Philosophical Logic' [Princeton 2009], p.37
A Reaction
This is my reaction to the modal cases as well - the absurdity of thinking that no actually nonexistent thing might possibly have existed, or that the actual existents might not have existed. Williamson seems to be the biggest friend of the formulas.