That is why the appeals process will presume that the authors of the code intended it to make sense. It is a basic principle of law that the writers of the rule in question did not mean to require what cannot be done nor to forbid what must be done. Since you must apply solder to the conductors in order to fuse it to the metal the code cannot be construed to make that impossible. The code language is only intended to prevent the use of solder as a means of mechanical attachment of a conductor to a terminal or for the mechanical stability of a splice. A mechanical splice is "mechanically and electrically secure" without solder but it will not remain that way if you do not solder it. In the absence of solder the connection will corrode and open due to thermal cycling. Once soldered the connection is protected from corrosion and the effects of thermal cycling are minimized by the heat sinking qualities of the solder.
-- Tom H