Cardiovascular diseases are the number of cause of death worldwide BY FAR. Millions of people die every year from consuming fast food. Fast food does not really serve a purpose apart form being tasty/quick/cheap. You could fulfill your dietary needs much better with different food.

Should McDonald's be banned? I do not think so. Anything can be misused.

To answer your question about what "good" uses there are for deep fakes: Cheaper and better special effects, available to a MUCH broader audience than before. I cannot even imagine all of the great use cases creative people will find for this.