§ This quote, popular with a great many cynical people, is from the William Shakespeare play Henry VI, Part II. At this point in the play Jack Cade and his followers are proposing to replace the rule of law with the rule of personal whim, a dictatorship.
Henry VI, Part 2 act iv: scene ii:
Cade: There shall be in England seven halfpenny loaves sold for a penny; the three-hooped pot shall have ten hoops; and I will make it a felony to drink small beer. All the realm shall be in common, and in Cheapside shall my palfrey go to pass. And when I am king -- as king I will be -- there shall be no money; all shall eat and drink on my score; and I will apparel them all in one livery, that they may agree like brothers, and worship me their lord.
Dick: The first thing we do, let's kill all the lawyers.
Cade: Nay, that I mean to do. Is not this a lamentable thing, that of the skin of an innocent lamb should be made parchment, being scribbled o'er, should undo a man: Some say the bee stings; but I say, "tis the bee's wax: for I did but seal once to a thing, and I was never mine own man since."
§ What is going on here? Well in this play Cade is plotting to overthow the king at the behest of another claiment, the Duke of York, who wants instability in London so he can be the strong leader who saves the day. He has a mob of followers, including the speaker of this famous line Dick the Butcher, that he has charmed into following him. Shakespeare means him to be ridiculous and this is a commentary against those that would kill all the lawyers.
§ It was at least as common in those days as it is now for groups of ingorant people to be resentful of the power held over them by the rich and educated. Much of the time they idly chitchat about taking over the country and getting even with various groups. The law is against them in their minds because they cannot see how it benefits them, only that it prevents them from doing what they want. (Like driving when drunk, shooting guns at anything that moves, getting in fist fights with anyone that looks at them the wrong way, and the whole vengeance thing.) Of course lawyers are prime targets of these groups because they are educated, well off, and oppose them in court when they have broken the law. (Or cost a "honest" man too much.)
§ No wonder this line is still popular with so much of the militia movement crowd in America.