That's childish and goes against the spirit of debate. If you want to go into an argument with sources, bring your sources out right at the beginning. But don't demad they have sources, and and such state, explicitly or implicitly, that their arguments are invalid due to the lack of sources thereof, and immediately follow it up by bringing up your own unsourced arguments that are somehow more correct than theirs just because it was said by you. Demand sources, or don't. But play by your own rules.