The Know Nothings of the 19th century simply made up their assertions about diabolical catholic plots to dominate the world even though such things are in explicit conflict with the actual teachings of catholicism.
While I agree that these ideas are in conflict with actual Church teaching and that
the Church does not permit deliberate deception, the accusations were not simply made up out of whole cloth but were at least loosely based on theologians’ moral speculations and debates over the use of equivocations and amphibologies in mental reservation (a very practical concern in England prior to Newman’s time). Hence the reference by Blessed John Henry Newman’s accuser to St. Alphonsus Liguori, a defender of mental reservation (the wide rather than the strict variety).
Strict mental reservation was, as I understand it, actually condemned by Innocent XI, but some Catholics still debate about
what’s acceptable mental reservation. (Unfortunately, some Catholics even debate whether outright lying is ever justified-- cf.
Mark Shea v.
Peter Kreeft.
)
Spencer, on the other hand, points out the example of Muhammed himself in using deception to placate the enemies of Islam and buy time for the faithful to become strong enough to wage jihad on the infidels.
As I’ve heard the Ishaq story related, it’s Nuaym ibn Masud who asks Muhammad’s permission to lie, suggesting it’s not normally allowed. Muhammad encourages him to sow dissension among the confederates who are laying seige to the city and adds “war is deceit.” Nuaym ibn Masud is the one who creates the deception.
The Ibn Ishaq story is somewhat problematic as a religious source, because Muslim scholars of hadith (sayings & acts of Muhammad) and fiqh (morality, conduct, jurisprudence) question its reliability especially for fiqh. In light of that, I don’t know whether and to what extent Muslims would actually look to that story for personal guidance. The “war is deceit” comment is stated in reliable ahadith, but without Ishaq’s contextualizing story.
But I think there are probably more useful sources anyway.
In Sahih Muslim, considered by Muslims to be the second most authentic hadith collection, one finds tension between absolute honesty and some form of dissembling:
Sahih Muslim:
Chapter : The evil of a lie and the goodness of truth and its merit.
'Abdullah reported Allah’s Messenger (may peace be upon him) as saying: It is obligatory for you to tell the truth, for truth leads to virtue and virtue leads to Paradise, and the man who continues to speak the truth and endeavours to tell the truth is eventually recorded as truthful with Allah; and beware of telling of a lie for telling of a lie leads to obscenity and obscenity leads to Hell-Fire, and the person who keeps telling lies and endeavours to tell a lie is recorded as a liar with Allah.
On the other hand, there is this:
Sahih Muslim:
Chapter : Forbiddance of telling a lie and the cases in which telling of lie is permissible.
Humaid b. 'Abd al-Rahman b. 'Auf reported that his mother Umm Kulthum daughter of 'Uqba b. Abu Mu’ait, and she was one amongst the first emigrants who pledged allegiance to Allah’s Apostle (may peace be upon him), as saying that she heard Allah’s Messenger (may peace be upon him) as saying: A liar is not one who tries to bring reconciliation amongst people and speaks good (in order to avert dispute), or he conveys good. Ibn Shihab said he did not hear that exemption was granted in anything what the people speak as lie but in three cases: in battle, for bringing reconciliation amongst persons, and the narration of the words of the husband to his wife, and the narration of the words of a wife to her husband (in a twisted form in order to bring reconciliation between them).
According to the Muslim commentaries I’ve looked at, this is understood to allow dissimilitude in only three circumstances: in the midst of war, to reconcile people, and specifically to reconcile husbands and wives.
Elsewhere, it is suggested that some such acts should not be considered “lying.” In the most reliable hadith collection, Sahih Bukhari, it is said, for example: “He who makes peace between the people by inventing good information or saying good things, is not a liar,” (3.49.857). In commentary, this is often applied to the spousal scenario, for example, if a wife asks “Does this dress make me look fat?” and her husband replies “You look radiant.” Here, the husband says something good to avoid saying either yes or no and to maintain peace. And, having answered neither yes nor no, it’s easy to see why he would not necessarily be called a liar.
(cont’d)
First they were not intelligent enough for you. Then they were Christain’s with an agenda. I doubt anything but radical Islam itself in person will convince you. 
