As a Voluntaryist, mine is an outside perspective, but I'd still like to give a ringing endorsement to Frederic Bastiat's The Law, since it was the first popular political treatise, predating even Spooner's No Treason, to point out that what the state engages in can best be described as "legal plunder."
To my knowledge, Bastiat never carried this idea to its logical conclusion (calling for the abolition of all non-voluntarily funded forms of government), even though on his deathbed he did acknowledge the proto-market anarchist Gustave de Molinari - one of the very first economists to explore the possibility of a free market in defense and arbitration - as his direct intellectual successor.