Superman saved the human race from annihilation and was ready to come out in the open (hence Lois saying "welcome to the planet"). The Enterprise defeated Khan, Admiral Marcus was dead, and there is renewed optimism for the future. How did the heroes lose exactly?
Kirk was the one that led the Vengeance back to Earth, and released Khan from his cell. Kirk's crew got Khan on board a ship he had "inate knowledge of", as Spock said, lining him up to take over the Vengence, which Khan then used to kill thousands of people ... yeah, they prevented Marcus from starting a war with the Klingons, but it was at great cost - I wouldn't call it a victory, and Kirk all excited for his new five year mission at the end of the didn't jive to me, in light of the destruction his enemy had caused - a man he released from a jail cell - most people, no matter if they stopped the "bad guy", would be dealing with the feelings of guilt over the deaths the villain had caused, especially since they had captured him successfully, but then let him go. I would think Kirk would be questioning himself, wondering, "I wonder what would have happened if I had actually just turned Khan over to Marcus - would he maybe have spared my ship, regardless of what he said later? Or if I had run to another Federation area, instead of Earth? How many lives on Earth would have been spared, if I had just taken the ship to a starbase instead of Earth?". Kirk would likely have had to explain his reasons for releasing Khan to grieving families who lost family members in those skyscrapers... definitely not a victory for the Enterprise crew, and their smiles at the end of the movie don't jive with the tone of the destruction caused ...
Marcus made it clear: He was going to kill the Enterprise crew. So we get:
They hand Khan and the 72 torps over, Marcus kills everyone...
A) He starts a war with the Klingon Empire, costing countless lives--far more than the crash of the Vengeance--and Earth still still ends up on the firing line.
B) Khan kills Marcus, wakes his crew. Now we have a genocidal madman with a super ship that might get stopped but not before he scorches a good bit of the planet and kills God only knows how many Starfleet crew in the process.
Body count still ends up higher. They run to another sector, the above plays out the same.
By now, it would be normal to them. 6 billion Vulcans here, 100,000 San Francisconians there, who cares?
As the Joker said, it's all part of the plan.
Not to mention 7 million killed in the Xindi attack on Earth.
If you're going to attack the key world in your story, make it count.