Wuselkobold:
Yes, OSC hunts slavers cause they pirate Liners and enslave the passengers. If the corporation would do nothing against this, the passengers would consider other ways to travel - like hiring freelancers, wo are willing to fight for their freedom (cause they get paid only when the passenger arrives his destination).
In order to give passengers the feeling, that they travel fast, luxurious and secure trough Sirius, OSC has to hunt down slavers. Yes it is some kind of PR ... but without it nobody would fly with them (or only the poorest with no other choice). A good PR is important for any kind of business.
Not the freed slaves pay OSC - every passenger traveling with them because they freed some pays.