I think there is a huge difference between adult children coming home for a meal - whether it is Christmas Dinner or an informal supper - and going to a friend's house for a dinner party or similar. I don't really understand the thinking of those who seem to be seeing the two things as the same. Of course people should take a bottle or two of wine, or flowers/chocolates to a friend's house, but that's not the question being asked, is it?
If we have family parties (usually at my sister's house) for 'big birthdays' or similar, everyone brings something, but that is completely different as there is usually upwards of 30 people, and we comprise vegans, vegetarians, coeliacs and so on, and range from newborns to great grandparents, so if we all contribute something then everyone will get something they can eat and enjoy. That's not the same as an adult child and their partner coming for something to eat, though. Or not in my book, anyway.