As I've mentioned previously, this isn't about bio domes, Connor. Those generate an amount of food, which support the Zoners and whoever uses Freeport 9. The corsairs need all the food they can get, because they have a planet to support. A barren planet.
The most important fact is that it's an open marketplace, mainly due the fact that it's ran by the zoners. Both the Outcasts and the Corsairs use it, because it brings them goods they need closer.
I've seen that Corsair Council to Zoner Leaders transmission, and they were saying that they were denied the right to build a base in Theta. Well, do they have the resources to support such base? It would certainly be easier with the Zoner freeport around. If they take Freeport 9 and turn it into a corsair outpost, all those goods that were flowing from the Sigmas and Omegas will be cut off , leaving the Corsairs with Bretonia as their only supply line. (Cadiz - Leon - Tripoli).
Now, the Corsairs can roleplay whatever they want, but if they were to go through with this, they should be affected by it, because such move will harm their economy.