Very slight problem. You might not even notice it.
Taming humans isn't any different from taming equally sentient human-like creatures.
The idea that he could tame them is due to them being part animal. If he can just tame humans it means he can enslave a whole country or worse stop any villain by just enslaving them or something along those lines to stop them. Including the "Hero". But I suppose a work around would be the whole consent thing that all those girls have been giving to MC.
Has it been shown that he can enslave someone against their will?
If you can please tell me the others you've read
I suppose you are right. While I would personally think that taming would mean taming someone against their will just like you would do to rowdy animals in barn (hence the word taming not leadership). It is clear that this Manga isn't taking taming in that sense. So even the animals that he tames outside of the girls, I reckon are being done consensually.
I don't think there has been any instance of forced taming. It's always a willing exchange
