That kind of blanket statement is not only factually wrong, it does no one any good.
Almost all food consumed in the world is mass produced, and most staple foods (rice, grain) have been mass produced for centuries now. While we've increased automation in some things, using a robotic metal arm to harvest grain doesn't change anything about how healthy the grain is.
Now what sorts of pesticides are used can change things, but being "organic" doesn't change this, as some of the initial (early 2000s) organic pesticides were found to be horrifically toxic. Each substance applied to food needs to be judged on its own.
The real problem with food designed for mass consumption (different than mass produced!) is that it is engineered to be hyper palatable, so people want to eat more of it. Think potato chips (very few people ever open a bag of chips and have a reasonable number!) or any other "snack" food. Individually the ingredients may be safe (in moderation, and note that plenty of "healthy" foods are bad for you in excess), but when packaged together in a way that encourages over-consumption (and then backed by an ad campaign that does the same), negative health effects start to appear.
And FWIW plenty of "highly processed" foods are healthy, the issue once again comes down to most foods in the highly processed category also being engineered to encourage over-consumption. However things like whey protein are highly processed and healthy.
All that said, eating nothing from a bag or a box or a restaurant will generally improve a person's health, but that is largely due to the reduction in calories.
