Isn't the basic idea to preachy for today's audience?
As I've argued in other threads, my gripe with "Assignment Earth" or THE QUESTOR TAPES is the patronizing treatment of humanity as a child that needs constant nannying. A child needs to make mistakes to be able to mature, however all these "superior" aliens are not our parents. What makes the aliens superior anyway? What is "right" for them may not be right for us.
TREK's Prime Directive is a great idea, even though everyone seems to violate it. (I know, they did it to save the ship. But in "Bread and Circuses" Spock admitted that the ship and crew were considered expendable to preserve the Prime Directive.)
THE GREATEST AMERICAN HERO was, in a way, similar to "Assignment Earth." The difference is that Gary Seven was effectively an alien (human stock, alien upbringing), while Ralph Hinkley and Bill Maxwell were totally human. Ralph and Bill (polar opposites) were given leverage, but how to apply it was up to them. (Fans of the show know that the aliens briefly stepped in during the third season to tell Ralph and Bill that they were flubbing their mission.)
Still, managing individual crises doesn't do much in the long run. Cops arresting perps doesn't address the root cause of crime. And well-intentioned "social programs" often make things worse.
So, if a race isn't allowed to make its own mistakes and learn from them, they will become perpetual baggage, eternal children. And if they make mistakes too big to survive, that might be for the best.
In the novel 2001: A SPACE ODYSSEY, Arthur C. Clarke described advanced aliens as farmers in the fields of stars—"They sowed, and sometimes they reaped. And sometimes, dispassionately, they had to weed." This suggests that intelligent life is abundant. It also suggests that the aliens had some ulterior motive, which Clarke addressed in CHILDHOOD'S END.
So why are Gary Seven's people tinkering with Earth? Because it gives them a warm, fuzzy feeling?
"Beware of altrusim. It is based on self-deception, the root of all evil."
—from THE NOTEBOOKS OF LAZARUS LONG
EDIT:
DOCTOR WHO is typically helping Earth fight off alien invaders, not cleaning up Earth's own messes—although there have been such episodes. It depends on which Doctor you choose. Pertwee spent a lot of time on Earth.