Emerikol
Legend
There is something that people forget. Sandboxes are *boxes*. Boxes have sides. There is (implicilty or explicitly) an agreed upon play area, and your'e expected to stay within it. If you step out and go over to the basketball court, well, that's your wish, but you are clearly outside the sandbox.
An adventure is a sandbox if, within the context of the adventure, the players are free to do what they wish.
A campaign is a sandbox if, within the bounds of the campaign, the players are free to do what they wish.
So, the adventure can be a sandbox. If, however, they players can't say, "giants are dumb, let's go do something else", then the campaign is not a pure sandbox, even thought the adventure still is one.
Umbran beat me too it.
I would of course give some clues at character creation about the type of sandbox I was creating so that if an all rogue group didn't make sense the party would know that. A sandbox does not have to have everything in the universe in it. It just has to allow the PCs to do whatever they want within it.
I'm not even anti-designed adventures. I just prefer they be offered within the context of a sandbox setting and the players can opt in or out as they please and they can quit whenever they want too. Of course sometimes that means consequences inside the campaign but that is okay.