Just my two cents as someone who was watching the conversation in the thread it seems like this is the way you should talk about it. Focus on this, the events of that timeline were erased, they never happened, and never will, and the events in the 8 years between the start of this game the start of that one will change the character so that, while they share a name and a likeness, they will be totally different people who wouldn't ever make the choices that in that timeline caused the option for NTR in the first place.
And just as an aside, and speaking for myself and some others, the reason it bothers some people even if it was optional is because it speaks to those characters that were involved. If I may give an example, I'll do it in a spoiler tab so as not to bog down the thread and in case you'd rather not read it, but it'll be there if you do:
Anyway, all that to say, I do think that the "old game's timeline is erased and has nothing to do with this one and couldn't ever happen as it did in the first game," is the only real tactic to take. And even talking about the old game being "optional," only adds to confusion since saying "it is optional," implies that the old future could still be possible. Which, in my opinion, if you want any hope of attracting harem fans it needs to be made clear that the old future is not possible at all, not just optional and things could still end up there.
It also precludes a third of them even knowing about the other two-thirds. I guess that lowers the possibilities of jealousies.
