In light of recent events, I believe we need to streamline the role of the BH.
Here's my suggestion to do that:
1) The standard Bounty Hunter hunts for bounties throughout the Sirius Sector (with the exception of Kusari). His/her source of income comes from bagging the bag guys. They may use any ship class from LFs to gunboats to get the job done (ship class guidelines will be in the new ID in any case).
Pirates may not ply their trade in anything larger than a gunboat, so the same should apply to the BH.
2) The Bounty Hunter Guard pilots may hunt for bounties if they are piloting anything from a LF to a gunboat. Bounty Hunter Guard capships (in this case a destroyer/BC/BS) may not claim any bounties nor participate in a bounty hunt. Larger ships are reserved for operations against the Order and the Nomads.
However, the BH capship may defend itself if fired upon (Corsair capship/bomber group opens fire first) or if the rp situation calls for engagement if diplomacy fails (another pilot is firing on BH npcs and/or has BH pilots in his hold). Of course, if the "offending" party is trying to fix rep and has to kill BH npcs to do it, then it's reasonable to turn a blind eye to his activities.
So, if you strip away the ability for a larger capship to hunt bounties, that would make the BH side think long and hard about launching any large scale assault on Gamma. They couldn't be there for bounties, so another reason to be there has to exist (an rp reason, prearranged battle, etc.).