One of my sisters went with us on our vacation, and her help was invaluable. She has also recently discovered that she is lactose intolerant. Believe it or not, this puts her in the majority. Most people across the world (aside from Northern Europeans) have some form of lactose intolerance after childhood. Yet cow's milk is prevalent throughout American culture/cuisine (at least).
It was interesting trying to find restaurants/places to eat with lots of options in addition to meals prepared with milk, cheese, butter or cream cheese. Try it sometime - it's actually pretty difficult. Desserts in particular are usually made with butter or cream (or both). Lots of restaurants have "melts" - sandwiches with cheese, salads with cheese, etc. It's true, you can request cheese not be added...but that's another step to the process.
Another friend of the family is allergic to soy. This is another ingredient that seems to be in everything! You wouldn't think that soy would be included in pre-made cakes, chips, etc. But as you look at labels of various processed foods...it's there.
The tension between what's convenient, and what assumptions the majority makes has always been fascinating to me. I would have never thought about asking some fast food restaurants if they fry things with butter - but now that I'm conscious of it - I might. I've also never thought of asking if soy is included in a list of ingredients.
I believe it is worthwhile to ask what is in the food we eat, and also where it comes from.