At present industrial countries spend between 9-11% of their annual income on foodstuffs and less than 5% of their time gathering said foodstuffs - the lowest in time/money expenditure for food in the history of the world.[1]
If we die slightly earlier due to a possible rise in cardiovascular disease then it was a small price to pay for saving years in productive time.
Also, fast food firms are an easy target but when pressed for an answer, the team at Freakonomics made a pretty good case that a McDonalds hamburger is possibly the greatest foodstuff when balanced between cost, speed, safety and bountifulness of nutrients.[2]
The real problem with convenience food is not the nutritional content (which is perfectly adequate and superior to most diets across a historical timeline)is the unsustainable agricultural and water scarcity burden it places on the planet.
[1]http://www.npr.org/blogs/money/2012/06/08/154568945/what-ame... [2]http://www.marketplace.org/topics/sustainability/freakonomic...