I believe that quote was by H. L. Menchen
Yep....however, in the context of his famous quote, I think he was actually talking about how one would go about overthrowing a country and that “killing all the lawyers” would be the first step to prevent the lawyers from stopping an overthrow. IOW, they were viewed as a valued stalwart rather than the real problem they are today.
From Wm. Shakespeare - Henry VI.