That sort of adversarial bollocks is a bit shallow and something I would never bother with.
I have two employees that came back after leaving - you?
I would, however, try to obtain the same info using less jarring questions; possibly asking why the employee chose _us_ to decide to make their next career step, what inspires them to do this work, things like that.
The original question is already a red flag. Now we're just taking jabs at each other. Especially if this is an interview after I've given you a technical test which probably represents the work better than any answer I could give to the question.