RAR sacrifice problem

[Atahualpa]

I have a problem with the Rise and Rule mod v1.02. It says I should be able to sacrifice this slave worker, but the sacrifice button doesn't appear.
I am celtic and I have ritualism.

The ritual sacrifice improvement is said to only double the effect, but not be necessary.

I have so many enslaved workers, I don't know what else to do with them.

[Atahualpa]

Btw, this is a game on emperor level. I hardly had any luck so far winning on emperor and it looks tough this time as well. All of the three AI players on my island are just so happily united against me
When I first encountered them they were all annoyed (not that there'd be something like curious) and after some time they came in with demands. I fullfilled some of them, because I wasn't ready for a war. So I built up a military and told them to leave my territory. Ofc they got even more annoyed and declared war. Mostly the orange ones (ottomans). I managed to get peace (had to pay them) and at some point they even showed up as "polite", but they entered my territory again, I told them to leave and they declared war again (from polite to furious).
Then I was on the verge to get the gallic swordsman, so I thought **** them all, heavily producing archers and then this unit and went for war against the persians.
Now the zulus have joined and so I currently wage war against all of them. Great.
OTOH, I shouldn't be troubled too much, my spearmen provide good defense and they hardly have any 2-move units and unless they learn to stack a defender with their fighters I take them out one by one.
The only trouble would be a culture flip and that's why I need to sacrfice the slaves (not in the city on the screenshot, but the captured one)

[Atahualpa]

Anybody?

[Atahualpa]

I got it for myself. Slavery is a required tech and I had not had it. Should be mentioned in the Civilopedia.

And my prediction was false the game's pretty easy so far. I was pushing out some Gallic Swordsman and then killing off anything the persians, zulu and ottomans sent against me. This was easy, since they always stopped one tile before my city and hardly stacked a defender with them. My 3 attack swordsmen had no problem with their 1 defense archers/swordsmen/chariots.
But now I made peace and ripped the Persians off of as much techs as possible.

Thx to sacrification the city closest to the persians now has more than 100 culture and I hope is much less likely to flip.