I wouldn't mind if an ex-prostitute is added to the harem as long as the manga doesn't make a big deal out of it. Unfortunately it keeps trying to explain to us why her being a prostitute isn't bad and we shouldn't judge her based on that. Except that this girl decided to be a prostitute by choice, sure she needs money to help with her family's debt but:
1. Why must she be a prostitute? There are tons of other professions available for normal female humans in this world. Sure she might make more money this way (which is never explained in the manga by the way but I'm leaving it here for the sake of discussion) but it is clear from the get go that the debt is so ridiculous it's impossible to pay off anyway so what's the point?
2. The whole debt thing started because the lord wants her to marry him. Are you really telling me that being married to an evil bastard is somehow worse than selling your body as a prostitute? What kind of stupid logic is this? I won't buy the explanation that prostitution doesn't have the same negative connotation as the real world because she keeps asking the MC if he would accept her despite her "dirty" body.
Add to that the fact she keeps feeling sad about being in this profession despite the fact she herself decided to do this when it wasn't absolutely necessary to do so and it just comes off as very dumb. I mean she can just quit anytime she wants because the brothel owner is apparently a good person and fully supports her in dealing with the lord.
As you can see as soon as moral and seriousness is introduced the manga becomes just as stupid as many of its peers.