SJS, To say that the difference between MO & Black hat is that MO doesn’t “assur the muttar” is off-base.
According to your logic, your Rav also assured the muttar when he said that you can’t eat starkist tuna, being that most other Rabbonim say that it’s muttar.
On many, if not most halachos in Shulchan Aruch there is a Machlokes how to pasken.
The difference between MO & black hat (in this regard) is that MO Rabbanim will usually pasken like the maikel side even if most acharonim pasken like the machmir side (obviously there are exceptions)) & in general find “kulos”.
So maybe you could say that MO “mattirs the assur”.
Now I know what you are thinking & we can go in circles till we turn blue in the face (or fingers) & end up right back where we started.
I think your comments & approach to to your friend with the food are foolish & absurd.
We don’t accept people who eat in treife resteraunts – PERIOD. (Sorry if I sound like Joseph on that one.)
It just so happens that the Chofetz Chaim (Klal 4)says that one SHOULD speak Lashon Hara about the type of person you describe.
It is the MO’s “acceptance” of such behavior which makes such a lifestyle less threatening to a potential BT.
As far as eating in her home – I am not a Rav – but I believe you are correct. (See, at least we agree on something! 🙂