There are plenty of extremely self centered bitchy mothers like Rachel IRL. There are a handful of unconvincted rapists IRL. I dont understand the gripe about "cartoonish villains".
F/D pure dad is definitely not a dick. There is unconditional love most definitely. Turning that into a romantic and physically intimate relationship is taboo and shouldnt be pursued for a number of reasons thats for sure. But he is a flawed human being, his daughter is a knockout (who he didnt raise), and she is innocent, virgin, naive at 18 which is rare today. Hey its a romance story that breaks taboos.
Incest is fundamentally flawed. God forbid if they get serious and have a long term romantic relationship and end up breaking up. Can you imagine having your dad (or mom) as an ex? Having children should be out of the question. Daughter should be encouraged to date someone her own age, who she doesnt have to hide or feel ashamed with, who she has a possibility of making babies with without a 25% chance for retardation or whatever the health risks are with incest...
The right thing to do would be to stop the boyfriend charade, but I think we can all understand the temptation and how hard that would be in this situation. The romantic in me enjoys the connection and I can understand the unconditional love from F/D turning into a cheesy romance love type thing.
Personally I have had a true love experience twice when I was a teen. It might be possible now as an adult, but adults are so jaded from day to day concerns like paying bills and working and whatnot. We dont trust or let our guards down as easy, and our sense of wonder, our imagination is blunted.
With the F/D unconditional love being a thing, taking it a step further by adding physical intimacy is a way to cheat the system if you didnt commit to your high school girl friend. This situation is a perfect storm of daughter not being raised by father and meeting all the naive criteria.
Now the harem playthrough dad is most certainly a dick and mom probably has a good reason for doing what she is doing.