So, as a Rogue Trader in the vast Koronus Expanse, you have at your disposal a powerful ship, potentially a regiment of troops, or more specialized forces, and an ego that requires a battleship, even though your mother only left you a light cruiser, as your flagship. Most of the planets in the Expanse are backwater primitives, with people who don't remember the God-Emperor, where the AdMech might be absent, et al.
Lets use Vaporius as a means to this silliness. I am playing Rogue Trader Lady Sun Lee, having just arrived on this little ball of sand. I am brought before the leader of this area, a Priest-King named Ansai; a man who believes himself to be a god, like he's a Gao'uld from Stargate. I'm rather used to getting lesser people to see my "divinity", as well, so I'll play this game with him. If I try to bandy words, he'll act tired and unimpressed. If I try to bully him, he'll not budge. If I attack, a flock of children will become as his shield; his troops will mobilize, and think to try and cut me down. In his own words, he's as a god, with the minds of all his people his to command, even to death. Still, I'm a goddess, too, and where he controls the people, I command the very skies; the earth itself trembles at my will. If I will it, the Nihontu can open fire, from orbit, and cause a pretty good earthquake. I might also disappear in a flash, and then my "holy light" will level his precious, glass city. The Priest-Kings of other cities will think twice before pitting their "divinity" against mine.
Well, what's to stop your players from derailing situations like this? A place like Zayth might certainly have resources able to defend themselves, as might Damaris (even on the far side of the planet from wherever the Bulwark might be, right then), but lots of those places might have no real tech, no gun emplacements, or void shields; if I leveled Ansai's city, there are several others, each as good as the last. Would these people, even the Priest-Kings, know of void ships? How do you make your players play ball, when they really can use "both barrels" diplomacy?