I think you guys have mostly summarized this topic pretty well. Harem is ultimately just a type of wish-fulfilment fantasy.
Now there are two types, harems and pseudo-harems.
When the author introduces girls but mc only chooses one, or when the mc doesn't choose at all and just conveniently ignores the fact that having a relationship is a thing, that is a pseudo-harem.
Most of these are bad bcause, the author introduces all these girl characters just to get them rejected. THis is mostly to conduct waifu wars, and lead to fans blaming the Mc for being a beta and not satisfying all the girls.
In my opinion, the fact that he didn't choose all means that he is an alpha, cause like just because all of them love you is not an excuse for you to betray yourself and just give in and please em' all.
Then there are harems, where the mc actively has a relationship with multiple girls. The thing here is, such a thing is not health but really toxic. Just like men, women are possesive to, so sharing means that they have underlying motives like being protected by your power, or something like that.
I mean all emperor's royal families are a fucking mess where half-brothers kill each other, Like come-on man isn't it obvious what the problem with harems is by now!!!
Those where the females do accept and are genuine often come off as sub-par characters and one-dimensional.
Like Honestly I don't get to understand why strong characters will agree to this stuff.
The only harem that has actually worked is I think, A will Eternal by Er Gen. The reason being, you don;t really care much about the female characters. Even if they are one dimensional and have very little screen time, they aren't the focus of the story. So it's fine.