[X] Plan Closest I Can Get To Diplomacy
And everyone knows that rebellion by the marines is a thing which never happens.
Oh wait, actually it's the exact opposite. Even beyond that, marines answer to pretty much nobody, follow their own traditions above imperial orthodoxy, and frequently put the good of their chapter above the official goals of the imperium. Even the inquisition gets told by marines to fuck off fairly frequently, unless said inquisitor is ready to throw a fleet at them. Diplomacy with the marines is something we really should keep on the table.
Besides, we are the weavers of life, and marines are eternally in need of more gene-seed. We can use that as leverage.