Actually rust can sleep, just remove the source of oxygen...
To better answer your question I need more information, are we talking heavy surface rust but not much pitting, or is it suface but heavily pitted, or do you have areas were the rust has penetrated all the way through the metal. Depending on your particualr circumstance your treatment options will vary and it will also depend to a certain extent on what you want from the vehicle. To answer your general question there are much better products than muratic acid. Give me some more details and I'll describe some options.
This Muriatic acid (Hydrochloric acid) thing was discussed in detail sometime back and it really is not a good idea. The Muriatic acid will remove rust but it sets up the metal for further corrosion and the process is nearly impossible to stop, in short DON'T get Muriatic/Hydrochloric acid anywhere near your car! Once the metal is contaminated with that stuff you will have big problems even if not apparent at first. Phosphoric acid works quite well and can prevent further rusting but the Muriatic/Hydrochloric acid causes the wrong chemical reaction.
assuming we are talking about a certain area on the car...say a quarter sized rust hole or something average like that....how is it impossible to cut that piece of metal out and replace it with new metal and not have effectively gotten rid of the rust?
What he is saying is, that there are areas of the car that you cant do that....and I agree. You can never get it all..........Unless you are on that Muscle car show, and they give you a brand new Camaro body.