So far as I can tell the AFA are using indirect and expanded view of the relationships within the sector to justify their actions in Bretonia.
Fair point, if this was an issue for people why hasn't anyone complained to date?
Take into consideration the perspective of the hyper nationalist movements of Kusari, and the expanded nature of the AFA.
Bretonia is currently the direct Enemy of Kusari, its opposition and rivalry as a dominant power within the sector has been building to this point for a very long time. Bretonia currently represents the last bastion of traditional agricultural production in the sector, Synth has taken hold of both Liberty and Rheinland, and is encroaching on Kusari now even.
With the expansion of the Empire into Northern Leeds it gives the AFA an asset to safeguard and stage offensive anti-corporate militant actions with the pretense of securing Kusari ideals. Those ideals mean the prevention of the expansion of SynthFoods into their territories.
Last I checked, Kusari has annexed the Norther quadrants of Leeds. From the perspective of a nationalistic Kusari militant I would call Leeds Imperial territory. If Leeds is then from that perspective a controlled portion of the Empire, then the AFA do infact have plausible justification to operate there.
Point two is that Bretonia and Kusari are at war, the AFA operates in the bests interests of the Kusari people as they see fit. They are a well trained and maintained paramilitary organisation. You're asking them to ignore a prominent and readily apparent threat to their homeland.
By interdicting and assault enemy supply lines they would be acting as a tangible deterrent to Bretonia's military operations within and surrounding what they would perceive as their sovereign territory acquired through honourable battle by their nation's forces. Through this they would be well employed to target what they would see as the most vital lifeline to the enemy that is seeking to hinder and assail their homeland.
The more weakened Bretonia exists as the stronger Kusari will reign, the stronger Kusari reigns the more prosperous that reign will be. Its through that sort of thinking that you can easily find justification for actions of this nature. Its all about safeguarding ones home, and securing its dominance and supremacy.
If Bretonia were to win this war then Kusari would lose, if Kusari loses so do the AFA, and from their view that means everyone loses to SynthFoods. So not only are they safeguarding their homes, they're also safeguarding the resources that could potentially be exploited by Synth and used for the further corruption of their people.
Its a matter of consider the ultimate and long term effects of the actions taken now and in past. This isn't restricted to one matter resulting with one end, everything is interrelated and as such reflects and influences each other.
Why is it so hard to understand that a nationalist militant group would be operating in what they would define as the best interests of their people within space controlled by their people and slightly beyond?