Take a look at the following political cartoon, in which a member of the audience criticizes a politician’s speech.
Why does this audience member want a citation? Because it's no secret that politicians sometimes twist the truth, give us unreliable statistics, and even make up things to support their points. We don’t trust what politicians say when we can’t check their evidence. That’s why major newspapers run “Fact Checker” columns that check the “facts” offered by politicians—and they find that their facts are sometimes wrong.
Of course, it's tough to add footnotes or a bibliography to a political speech. But these things are expected on your papers. If you want your readers to trust you more than they trust politicians, you need to cite your sources.