Full Idea
In Cantor's abstractionist account there can only be two numbers, 0 and 1. For abs(Socrates) = abs(Plato), since their numbers are the same. So the number of {Socrates,Plato} is {abs(Soc),abs(Plato)}, which is the same number as {Socrates}!
Gist of Idea
After abstraction all numbers seem identical, so only 0 and 1 will exist!
Source
Kit Fine (Cantorian Abstraction: Recon. and Defence [1998], §1)
Book Reference
-: 'Journal of Philosophy' [-], p.4
A Reaction
Fine tries to answer this objection, which arises from §45 of Frege's Grundlagen. Fine summarises that "indistinguishability without identity appears to be impossible". Maybe we should drop talk of numbers in terms of sets.