I watched a video version of die zauberflote with my wife a few days ago but had to switch off half way as she felt it was unfair on mothers!
how to answer that one?
I'd say that there isn't much of an answer to that; the opera is unreasonable to women, including mothers. Sarastro says that Pamina needs to be guided by a man, not allowing for the possibility of a different woman (or even Pamina herself having agency). Papageno is also a ridiculous character, who is after a wife... without regards to who that person is.
Then, on a different offensive front, we have Monostatos, the other villain of the piece.
It is a sexist, racist piece of work. This, unfortunately, does not make it stand out that much in the world of classic opera (or other art forms from the same time periods for that matter). I truly believe that this can be a significant impediment to enjoying opera for some people. I know I am very careful about operas I recommend others see.
Sometimes understanding and discussing the offensiveness can provide enough distance to enjoy the other merits of the work (such as the delightful music). Sometimes a production will have a different spin or de-emphasize some of the more problematic parts.
Kenneth Branagh's 2006 English-language adaptation
was an attempt to remove some of the sexist and racist implications of the text... but I don't believe they were entirely successful.
These methods will certainly not work for everybody or for every opera; if someone is offended by something turning it off (or leaving) is a reasonable option.