Maybe its like saying, a DM should restrict what they want, when they want, but they shouldn't be a jerk?
I think it’s more like « a DM should restrict what the group agreed on, when he/she sees fit, without being a jerk. »
The DM should at least propose *something* on session 0, which should give an idea of the themes and style of the game. Once the players agreed/accept that proposition, they should restrict themselves; the DM should act more as a councillor than an authority at that point.
If the players don’t want to play with those themes and the restrictions/paradigmes that come with them, then they shouldn’t accept to play that game in the first place. Move on an play with another DM or better still, discuss and suggest something else.
This is supposed to be something fun, why would anyone try to sabotage the fun of anyone? If two people can’t agree on what fun should be, then they should just accept that they are not compatible in that hobby, or work together to find a middle ground.
I know this is a bit more difficult when those dissentions slowly become more apparent as the game progresses but still, I assume a minimum of maturity from my DM or players (as they should expect the same from me).
D&D is a toolbox; you don’t have to use every single one of them. Just make sure everyone is having fun building.