I'll take just another fruit thank you. I guess I'm easy to please. Or maybe harem and incest are both my kink.
And of course that is fine, my friend. I am not questioning anybody's taste, never will I. I was just mentioning how I think that one item, people being happy about in an open harem, for me neutralizes the other, incest.
In my opinion, I enjoy it more if, for example, I am banging my family, but members are not aware, so that we have to hide and we have the risk of getting caught. That is a kink of mine.
In fact, hiding and incest works quite well, as it is a simple way to justify why your love interests are happy hiding the relationship so you don't get caught fucking several girls, which they would no like it: "baby girl, we being together is not something society will understand, so we must hide it from everbody, don't tell anybody, even your sisters (specially don't tell your sisters or they will kill me for being a fucking cheater)".
Without some taboo, you need another way to justify why your love interest don't open up to everybody knowing the sexual relationship.
Some games pull off the same taboo feel pretty well without resorting to incest, instead using things like adoptive family or step-family (Where the Heart Is, WVM), or by the object of affection being your best friend's sister (Being a DIK) or best friend's girlfriend (WVM), or by a professor-student relationship (several games), or by doing both the mother and daughter (My Sweet Neighbors, Polarity) or aunt and niece (WVM) even though you're related to neither.
I was just mentioning what is for me the reason behind incest. The concept of taboo as a forbidden fruit. You are mentioning others which satisfy the same concept. So if I understood you right, we are agreeing.
The rest of my comment was just mentioning what I think works as neutralizing the taboo effect on incest: essentially letting anybody be ok with it. In fact, that will also neutralize the taboo effect in your examples as well.
Some comments about your examples:
-Well WMV for me made the mistake in that everybody is happy in a big harem. In fact, I think that the overall visual novel is making no sense, every conflict is happily killed and everybody is just happy hugging. In fact, I called that the whole including the step mom into the harem, proposal her friend did to the MC was ridiculous. But hey, what do i know? I am overall disappointing in the novel right now. I thought it was going to be lot of sex and drama at university, not a silly "MC is a gift from the gods to women" harem
-Where the heart is I play it with incest patch as it makes more sense to me. I understand the mother figure not happy about banging MC openly for age reasons, maybe, but is harder to justify why the sisters hide it.
-Profesor student works perfectly, as you have an ethical problem. Who doesn't love naughty students?
-My sweet neightbours works really well, precisely because the closeness between the two heroines, which easily justify hiding the plot with the daughter. Pity is abandoned.
That is why I mentioned that incest is all about the forbidden fruit.
As always, just my opinion.