My point is simply this -- adding protection mechanisms and inheritance to classes neccesitates adding more complexity to the structure used to represent them (

My point is simply this -- adding protection mechanisms and inheritance to classes neccesitates adding more complexity to the structure used to represent them (such as a vtable) which does add performance overheads. If you dont need those features, you can go leaner and faster with a C structure that includes function pointers to give you the basic packaging of data and functions that an object has.