I mean I can't help but agree.
The reason I disagree with harem is because it's really just self insert. That's the only time it's enjoyable, and only to people who can enjoy having multiple girls and never deciding on one.
It makes no sense to me personally. And in the majority of harem series, the girls are so blindly in love with the MC for almost no reason. Just because he is the MC.
Rather than make me 'happy' or 'interested' this just makes me annoyed. It makes me like the MC less for being so undecisive or for not even noticing in the first place.
There is one series that I believe was a play on harems, and it was excellent - but it was only excellent when I saw the end of it. It was a series where basically the main character was actually just a scumbag who couldn't decide between the vast number of girls who were in love with him. However this series was much more realistic as far as the relationships - and most particularly the pain in which the girls experienced when they competed over the same guy.
There was a lot of drama, a lot of jealousy, a lot of hatred, and a lot of other bullshit. The MC then went from girl to girl (As you would normally see in any harem series), however rather than just playing it off this actually ended up severely hurting the majority of the girls in love with him every time he went from one to another.
They became terribly dependent on him as he swapped from one to another, just using them as tools, and in the end one killed him, and another killed the one who killed him.
This is the reality of harem. Or rather, this is what would happen if harem were to occur in real life. Not the silly little "Oh I went out with this girl and then that and then this one and uh yeah they were all just sorta fine with it" You can't just play with the hearts of people like they're toys without leaving any scars. This is what annoys me the most about series with harems. There are no permanent scars.