I personally believe that preserving a false and misleading picture of reality designed to trumpet a deranged cult that is working to make the world objectively worse for everyone including themselves is not acceptable.

I would say, "Look mum I love you more than anything in the world but preserving some of these movies crosses an ethical line for me."

Of course I grew up in a house of atheist jewish academics, so making and justifying personal ethical stances that contravene wider group stances is expected behavior in my family.