Dr. Schweitzer asks, "When did economists first equal government  
intervention with the use of force?"    
 
Weber defined the state as the institution in society that claims the right  
to use "legitimate" force in its dealings with other members of society.  I  
use a version of this idea and state that the state is the institution that  
"authorizes" the "legitimate" use of force.  The reason I emphasize  
"authorize" is because I want to allow for the Nozick argument (originally  
taken from Rothbard et. al.) that private defense agencies are possible.   
In my opinion Nozick's private defense agencies would still require some  
process in which it is decided when the use of coercion is legitimate and  
that process or set of institutions would be the state.  Hence, the  
anarachism discussed by these particular libertarians is a pseudo-anarchism  
since the main question of moral legitimacy still must be bridged. 
 
Prior Weber I would pick Hobbes as the "economist" (and I do consider  
Hobbes an economist in the sense of Mandeville and Smith) who first saw the  
state as prohibiting absolute liberty by the use of the threat and exercise  
of coercion.   
 
I am sure that careful research might turn up non-Western sources of  
earlier vintage (I suspect Chinese philosophers would have recognized what  
was so obvious about the state power under which they lived).   
 
A more interesting question is when an option placed before a rational  
utility maximizing action can be described as "coercive."   If I promise to  
give you a job that pays you 10 x your next-best opportunity but only on  
the condition that you first commit some outrageous act, am I coercing you  
to commit that act? 
 
Best wishes 
 
L. Moss