Of course, Jacob is getting a flood of "But Naofumi had no choice buy to buy a slave" and as someone who has watched several episodes, I'm going to dispell that counter-argument.
There is a very limited window that you could argue it was an "in-universe" necessary evil, but eventually Naofumi straight up gets called out on being a slave owner and through a rigged duel, he's forced to release his slave Raphtalia. Raphtalia then proceeds to argue how she's actually happy to be Naofumi's slave, and the people most invested in freeing her are portrayed as being self righteous.
Despite her being clearly in love with him, and he no longer even needing to have her as a slave, since she'd clearly remain his party member regardless, she chooses to become his slave again. And then he buys another slave on top of that who, surprise surprise becomes another waifu.
So yeah, the show starts to fucking indulge in that shit.