Why use Embryo Stem Cell, why not use Cancer cell?
 

Maybe we can cut out some Cancer cell... and put it in a special jar, let it grow. Maybe it will be an organ or skin cell for burn people.

Stem cells are a sort of blank slate for a cell that can be anything when "it grows up". Cancer cells are out of control cells that generally aren't anything useful (they are like having a rock in place of an organ). Hence why stem cells are so useful, and cancer cells are considered bad.