Players give feedback on the proposal. DM adjusts their ideas based on feedback.
Doesn’t build world until the players are agreed.
Or you have several players propose a campaign, the players vote on which idea they like best, and that player becomes the DM.
Players give feedback on guidelines, and they are modified if necessary.
Or they suggest what changes they would like.
The DM gives feedback on the proposed character, and suggests altererations that might make that character work better, or background details that can better connect them to the campaign world.
The difference between democracy and dictatorship is respect for others.