Indeed but that's still Tommy sharing his wife.
If sharing is then optional he won't be sharing her so MC won't be fucking her.
I don't think the sharing part is what's going to be optional, but the threesomes. Like I said, even if you reject the threesome, the MC still has sex with Abigail (no options there and I don't think anyone complained about that part), with both her and Tommy accepting that the MC doesn't need to agree in anything more at that point.
The main complain is how rejecting the offer for a threesome leads to a threesome anyway, just a day later, not so much how the MC still gets to bang Abi. I think people didn't complain much about the sharing aspect in general, because it seems that it won't be the main focus of the game. At least that's my understanding based on the dinner table conversation between "mother" and her "daughters" and that final scene in the cell.
Now, I obviously can't speak for everyone, but at least for me, someone who's not into sharing in any shape or form, it's easier to "tolerate" the type of sharing (again if I'm right and it's not the main focus of the game) this game offers, up until that forced MMF threesome, if it leads us to the "real" story.