So you're a great and all-powerful ruler with a burgeoning galactic empire. A payrolled mercenary, having the displeasure of depending on his services, has been ordered to stand down and await further instructions; last sightings of him settling on a nice little border world within your domain, tourist complex and everything. You'd even consider vacationing yourself were you not so busy in these trying times.
Now you're getting reports that the same outpost is on fire.
The little ***, left to his own devices for just two clicks has incited planet-wide unrest, costing untold amounts in both property damage and loss of life. It's an internal affairs catastrophe.
So: Why can't you just kill this clown? He's disgraced your empire and caused untold chaos.
A better question is then why oh why do I lose control of a planet when there is only a mercenary stationed there? I would understand were it to have become empty, as in susceptible to peaceful annexation and the like (having no political affiliation with me, the scum that they are), but neutral ( sans control marker)? It boggles the mind. Especially since this is the confirmed ruling in the FAQ. Madness!