Unless the "free the slaves" missions were eliminated only recently, they're still around - I ran one a couple of weeks ago. Of course, you only had their word for it that they were actually freeing the slaves. Mechanically, it was identical to any other smuggling mission.
Personally, I'd really, really like the ability to hand over "illegal items" to the local authorities. The only fines I've ever accrued have been for inadvertent smuggling, when I didn't bother to check whether the tobacco (or whatever) was legal in the system. I'd be scanned and fined on arrival, and more often than not, I'd find no black market there to dump the stuff. So now, I have to keep the junk in my hold and run the gauntlet again when I leave - and likely pick up another fine on the way out. I'd like the ability to go over to "Contacts", and click on "Hand over contraband goods to Police". They wouldn't fine you for doing so - but you wouldn't get any money either. I'd much rather make the loss than cop another fine.
Doing that, in a starport where slaves were illegal, would qualify as "freeing the slaves" in my opinion.
