"Excessive extraplanetary influence is even more vague. Historically, the Imperium has tolerated the use of force as an necessary outlet for built-up political and social pressure. In such cases, a short war is deemed preferable to continuing tension, sabotage, political agitation, etc. However, attempts by extraplanetary forces, such as offworld governments or large commercial interests, to seize control of a world's affairs is beyond the "safety valve" rationale.
"Assistance" is tolerated so long as it is deemed appropriate to the level of legitimate interest in the affairs of the world held by the extraplanetary organization. For example, the Imperium has often tolerated the provision by megacorporations of training cadre, arms, equipment, etc., on a limited scale, and even of training fully equipped striker units to local governments. However, when it has appeared that the primary burden for the conduct of the war has been carried by an extraplanetary power, the Imperium has intervened, claiming the power is using the misfortune of a local dispute as a pretext for aggression."
[MT:Imperial Encyclopedia, p. 28]
I think there is some evidence that this is propaganda and not the way the Imperium actual works.
If it can be assumed that the Imperium's worlds were generated by the standard UWP rules where government type is concerned, then how can the above be true when a shade over 10% of the worlds that can be rolled up have the government type '6', aka "captive governement"? This result is also skewed slightly towards larger populations with pop-6 having the best chance of being captive.
The word "captive" strongly implies a police or military occupation as captives are usually governed by coercion.
If a member world of the Imperium is the occupier, then the above quote is a fallacious bit of propaganda and opens the idea that the Imperium may allow tiny pocket empires as members because the Imperium hasn't stepped in to prevent or reverse "attempts by extraplanetary forces, such as offworld governments or large commercial interests, to seize control of a world's affairs"
If the Imperium itself is the occupier, then that suggests a fair amount of counterinsurgency actions as well as making the idea of autonomous rule for member worlds more of an illusion; do as we say, or the armed forces drop by until you decide to see reason. Is it possible that ~10% of the worlds and a slightly higher percent of the population are members of the Imperium against their will and are forced to join (wars of pacification)?
Naturally, Imperial Nobles act to oversee the worlds under their 'control' and to keep them under control using the armed forces at their disposal, when necessary, to ensure this happens.
I feel that Mike Wightman is absolutely correct.
Keep in mind that megacorps will do their utmost to keep their stockholders happy and given that the Emperor is a major stockholder in most/nearly all megacorps, and the Imperial Family hold still more power in megacorps' boardroom, and that the Imperium is unabashedly imperialistic, it should be a no-brainer that Imperial policy heavily favors megacorps over member worlds.But then, the Imperial family and local nobles often have shares in the megacorporations so its fairly obvious where their political loyalties will lie.
The Imperium's goal to "protect interstellar trade, to encourage travel and commerce" favors the megacorps in that the megacorps, who exist to make money off of "interstellar trade and travel and commerce" and control the greatest majority (nearly 100%) of the market benefit directly as a result of this policy.
Expanding these markets was the primary purpose of the Pacification Campaigns which allowed the Sylean Federation to grow into the Third Imperium.
If the various 'captive' worlds are occupied by Imperial Forces in the form of counterinsurgency or police action deployments, then perhaps those Pacification Campaigns are on-going as governments and public opinions shift on member worlds.