In a democratic China the Uighurs will have representatives. If they don't, it's not democratic yet.

Ask other democratic nations if they can get away with voting for systematic oppression of a people via a vote.

Historically, decentralizing power (i.e. via democracy) leads to less shittiness for more people.

In any case, what possible reason would the average Chinese person have to systematically oppress the Uighurs or falun gong? They're only oppressed now because their religion poses a threat to the cultural control the Party exerts over the people. In a democracy, that control vanishes.