This tiny and very simple submod practically (though not really) removes the slavery system.
Effects:
- captured enemies that are "enslaved" don't add to the slave population
- looting cities does not add to the slave population
The result is that you have a diplomatically neutral option for dealing with prisoners and you can get money out of conquered towns, all the while without worrying about a slave population that will revolt every two minutes. Obviously, this also means that you don't get an economic boost from slaves.
It's save-game compatible of course and probably doesn't have to be loaded before DeI, but it won't hurt.
Remarks:
I originally went out to lower the public order penalties from having a slave population. I could not find a thing, however, and so went with this solution. If anyone knows where to find what i originally looked for, please let me know!