I dislike harem, that's all.
I don't need to cater to literally every person in the world, and there's already plenty of "harem" eroge out there, so I don't see the problem.
Never said there was anything wrong with your game or what you like or don't like, so you don't like harems, that's fair.
But you're gonna get all sorts of people like this requesting what they want and the best thing to do is simply just ignore it instead of taking it personal. That guy will leave, he's not your problem anymore but replying to him saying you don't like what he does like creates conflict and no one wants that and also potentially alienates other customers or fans that may be into that too thus turning them away.
Basically be more professional about it and don't get personal.
Hope your game succeeds and you get plenty of success <3