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And here's the Wikipedia page about the incident, which has more details:

On 29 April 2013, the Boeing 747-400 operating the flight crashed within the perimeter of the Bagram airfield moments after taking off, killing all seven people on board.

The subsequent investigation concluded that improperly secured cargo broke free during the take-off and rolled to the back of the cargo hold, crashing through the rear pressure bulkhead and disabling the rear flight control systems. This rendered the aircraft stuck in an uncontrollable pitch-up attitude and induced a stall, and made recovery by the pilots impossible.

So it's not just unsecured cargo, but unsecured cargo that disabled rear flight control systems. I'm guessing unsecured people wouldn't cause the same problem, but it could certainly cause other problems.