Full Idea
Set theory is not innocent. Its trouble is that when we have one thing, then somehow we have another wholly distinct thing, the singleton. And another, and another....ad infinitum. But that's the price for mathematical power. Pay it.
Gist of Idea
Set theory isn't innocent; it generates infinities from a single thing; but mathematics needs it
Source
David Lewis (Parts of Classes [1991], 3.6)
Book Reference
Lewis,David: 'Parts of Classes' [Blackwell 1991], p.87