I've come across this phrase - "a diabolical liberty" - a few times recently, most notably in a Jeffrey Archer book. I've never heard it before. A Google search comes up with some bands, comics, and movies, all from the UK, which, combined with Archer's use, leads me to believe it's from across the pond.

Am I to assume it's approximately equivalent to "giving someone enough rope to hang himself" or a "double-edged sword"?

Is there any known etymology?

here's an entry for diabolical from OED2 which you may find to be helpful:

3. slang. In weakened sense: outrageous, disgraceful; disgracefully bad. Also, used as an intensive, esp. in diabolical liberty.
1958 B. BEHAN Borstal Boy III. 231 Why ain't I given a chance to follow my trade in 'ere, eh?..It's a diabolical liberty. Geezers get no chance to follow their trade. 1965 Listener 30 Sept. 507/2 A parody piece..which took diabolical liberties with Eurovision song contests, British Beatlemania and other suitable themes. 1972 MITTON & MORRISON Community Project in Notting Dale 69 The names he called those kids round there was diabolical for any vicar. 1982 S. TOWNSEND Secret Diary A. Mole 94 Asked our postman about communications between Tunisia and England. He said they were ‘diabolical’. 1986 Observer 16 Feb. 50/4 From my point of view that pitch was dangerous. In fact, it was diabolical.

I wasn't sure that I'd ever heard or read carnal license, but maybe I had; an exact wording Google search fetched 182 results. Might diabolical liberty and carnal license be alike in meaning, sometimes anyway?

" The peasants mistook spiritual liberty for carnal license."
- Schaff, VII, §75, "The Peasants' War: 1523-1525"

"My opinion is that it is better that all the peasants be killed than that the princes and magistrates perish, because the rustics took the sword without divine authority. The only possible consequence of their satanic wickedness would be the diabolic devastation of the kingdom of God. "
(Letter to Nicholas Amsdorf at Magdeburg, from Wittenberg.)

From here "carnal licence" looks more like "licence to kill".
( 007 again )

Both quotes concern Martin Luther's reaction to the peasants' uprising in (from memory, don't quote me on the date) ca 1525. "Carnal license" means giving free reign to 'the flesh' (which means the sinful human nature). The peasants, in Luther's view, were simply venting their uncontrolled hatred and fury in an orgy of violence. Though he didn't recommend either, Luther preferred even Tyranny to Anarchy, since at least in Tyranny the basic infrastructure of society remains intact, and there is less bloodshed. Maybe if Luther was President of the US in 2002 the course of recent history might have been different...

I wonder if diabolical liberty might be another expression for the tendency of the Neocons to circumscribe our "liberty" with restrictions intended to promote our comfort and safety but which in the long run restrict our freedoms (Luther's 'anarchy'?), tending to the creation of a police state (his 'tyranny'?)

That's what I thought, more or less, and all the defs flummoxed me! It seemed to be a deliberately oxymoronic phrase, pointing out that while freedom is highly desirable, it also has its "diabolical" drawbacks. :0)

Those who wold give up essential liberty to purchase a little temporary safety deserve neither liberty nor safety--Ben Franklin

I suppose the original (and literally diabolical!)concept of "diabolical liberty" (though not the phrase itself) is that offered by the serpent in Genesis 3. The knowlege of good and evil gained by an autonomous declaration of independence from God comes at the price of suffering the consequences of becoming evil, namely estrangement from God.

Ironically the Iraq War/"War on Terror" seems to have achieved both simultaneously. In Iraq it has resulted in Anarchy in the name of providing Liberty from Tyranny. And in Western coalition countries it is resulting in a drift towards Tyranny by the erosion of Liberties in the name of protection from the forces of Anarchy. Oh what tangled webs...

"That's a diabolical liberty" was a catch phrase scripted for Sid James in the highly successful and influential BBC comedy series of the mid 1950s, 'Hancock's Half Hour'. Typically, "They can't do that! That's a diabolical liberty"

WELCOME

I'm pretty sure it has a theological origin - it really means "of the devil". You can see these ideas clearly laid out in Milton's Paradise Lost, for example. God has permitted Free Will, because obedience and worship of God are only meaningful if we have the option not to obey or worship. But the exercise of Free Will led to the fall of the rebel angels, who have now become diabolical. But through continued use the phrase has lost most of its intensity, so "diabolical" becomes a mere adjective meaning "outrageous" or "offensive".

Also, the "liberty" part - "taking liberties" meaning behaving with inappropriate informality, in a presumptuous way. So a "liberty" would be an incursion on someone's privacy or dignity.

Diabolos (toy) evolved from the Chinese yo-yo, which was originally standardized in the 12th century. Chinese yo-yos have a long thin axle, with disc-shaped wheels, while the western diabolo is more cone-shaped. Diabolos are made of different materials and come in different sizes and weights.
The term "diabolo" was not taken from the Italian word for "devil"—"diavolo"—but was coined by French engineer Gustave Phillippart, who developed the modern diabolo in the early twentieth century and derived the name from the Greek dia bolo, roughly meaning 'across throw'.
The Greek word "diabolos" means "the liar" or "the one that commits perjury", from the verb "diaballo", which means "to throw in", "to generate confusion", "to divide", or "to make someone fall". Later the word "diabolos" was used by Christian writers as "the liar that speaks against God". From this meaning come many modern languages' words for "devil" (French: diable, Italian: diavolo, Spanish: diablo, Portuguese: diabo, German: Teufel, Polish: diabeł).
Confusion about the provenance of the name may have arisen from the earlier name "the devil on two sticks", although nowadays this often also refers to another circus-based skill toy, the devil stick. (wiki)