Full Idea
If one wants the quantifiers in each world to range only over the things that exist in that world, and one doesn't believe that the same things exist in every world, one would probably not want the Barcan formula.
Gist of Idea
Reject the Barcan if quantifiers are confined to worlds, and different things exist in other worlds
Source
Max J. Cresswell (Modal Logic [2001], 7.2.2)
Book Reference
'Blackwell Guide to Philosophical Logic', ed/tr. Goble,Lou [Blackwell 2001], p.151
A Reaction
I haven't quite got this, but it sounds to me like I should reject the Barcan formula (but Idea 9449!). I like a metaphysics to rest on the actual world (with modal properties). I assume different things could have existed, but don't.
Related Idea
Idea 9449 The plausible Barcan formula implies modality in the actual world [Bird]