That makes sense, if MegaUpload ever goes back up again - doubtful. That makes sense, if the feds return people's private intellectual property - doubtful.
This is more like the FBI burning the warehouse to the ground, with everyone's stuff still inside.
In a physical warehouse, keeping people's property would be considered theft as it deprives them of the property. In this case, it's only a copy of the data so there is no theft.
The feds didn't create a copy, they seized possession of an existing copy and took it offline. That actually deprived users of the contents (at least those who didn't have another copy elsewhere).
If you've a militaristic mindset, and there's a bad guy in the warehouse, this is exactly what happens. A siege mentality, and the simplicity and effectiveness of execution reinforce the approach.
This is more like the FBI burning the warehouse to the ground, with everyone's stuff still inside.