This is laughably wrong. They aren't converting that matter to energy - they are just utilizing Newton's third law. Throwing the matter really fast exerts an op

This is laughably wrong. They aren't converting that matter to energy - they are just utilizing Newton's third law. Throwing the matter really fast exerts an opposite force in the other direction. As far as human energy production is concerned, e=mc^2 only comes into play in nuclear reactors. Edit: to elaborate a bit, rockets are still just using stored chemical energy and converting it to kinetic energy. They're not converting matter to energy (i.e, using e=mc^2). It just so happens that stored chemical energy is loads more efficient than anything output by a laser (at this point in time).