At least he is not bending the truth. He is literally brainwashing and corrupting everyone aside from the first maid. He is a scum. Not a lovable kind. Just scum. The supposed happy go lucky vibes are kinda out of place though lol. Hero has a legit cause to kill his ass though of course it wont happen.
Conversely, he's operating within the restrictions of the world he's been put in, when he's on the "evil" side, and has managed to not murder the various heroines while finding ways to stay alive, and even helped some of them avoid worse fates.
The Cat Maid and the Innkeeper would have had
very tragic endings if he hadn't converted them and won them over. He prevented the sisters from being separated by "sides" in this war, and he also isn't...y'know, actively torturing and abusing them.
Yes, the premise itself is morally questionable, but in-setting, he could be a hell of a lot worse, and the choices he's made are what I would argue as morally-upward as could be expected, for the most part.
Going "he's scum because he's corrupting them and turning them into monsters" is just rejecting the entire premise of the plot and narrative and world, and his role within it, based on criteria that aren't inherent to the story the author is trying to tell.
In the abstract, sure - this sort of thing isn't great. But the "happy go lucky vibes" aren't out of place, because of the context of what's going on, and the erotica and "corruption" are integral parts of that, because ultimately he's actually doing what he can to stay alive, while not going full rape/murder/pillage like others on the Demonic side are doing, and that's been shown more than once.
It's fiction.
You don't have to "buy in" to the premise and can freely judge it based on whatever external moral framework you wish, and I'd strongly argue keeping that sort of thing in perspective is important even if a person enjoys storytelling like this, to ensure that the "fiction" stays exactly that. But condemning the characters based on that external moral framework doesn't seem fair, because it's not the framework of the reality in which they exist, and they have no agency to change or affect it.