Warpstone Meteor says (paraphrasing here do not have card with me) "Each player MUST (MY EMPHASIS) corrupt a unit in the corresponding zone or take a point of damage to their capital.
This has raised the question if the player has a unit in the corresponding zone can they elect to take the damage and keep the unit uncorrupted. There are other cards with slightly different wording (inserting the word "either") which more clearly suggests a player choice between effects.
I have not seen an "official answer" in any of the threads so I e-mailed Nate about it last night . Will post here when I get a response.