[spoiler] In the climax of the movie our hero returns the movie the next day and purchases a soda and bag of pretzels from the adjacent vending machines to celebrate the $2 he just saved. [/spoiler]
Now if they could remove the O2 and put that back in the air and dump the remaining Carbon down the tubes, well in a few million years we'd have lots of diamonds.
And once you've finished burying the carbon we could immediately start mining it to burn (combine with oxygen to release energy) in existing coal (aka carbon) burning power plants!
They won't or can't, so there is no use in investing lots of time and effort into this type of project.
As long as we get energy by burning naturally sequestered carbon based fossil fuels in solid, liquid, and gaseous forms and producing gaseous CO2 we will be fighting an increasingly inefficient uphill battle.
You are spot on using Slashdot as an example of how to achieve the same effect less intrusively.