I disagree. The MC's nature is very much an open question, at least for the moment.
It seems clear he is a demon, but we know there's a lot more to his past than Astofiel and Julia have revealed. We're also told the MC can survive and thrive in a condition that a demon shouldn't be able to. It's not unreasonable to think the MC doesn't work as advertised, in which case he might be able to draw power from his LIs in ways that don't involve converting them to sex toys. There's certainly no guarantee it will play out this way, but there is some support for the idea within the game. I'm hoping for the best, but we'll just have to wait and see.
Also, as an aside, I don't understand why "voluntary" consent matters. If demons slowly intoxicate humans by their very nature then any consent given by a worshipper is by definition invalid. Maybe Asotfiel is just used to fighting a propaganda war with the angels and thus reflexively puts a partisan spin on everything?