The only sect ascribed to Islam that deems is permissible to lie, abuse and literally defaming and accusing their opponents of falsehood (i.e. lying upon them) is the Twelver Shia sect. This shall be proven with ample evidence.
What Shia narrations (deemed authentic by top Shia scholars) say
Al-Kafi by Al-Kulayni vol. 2, ch. 159 ‘Sitting/Associating with Sinful People’, pg. 375, hadith #4
مُحَمَّدُ بْنُ يَحْيَى عَنْ مُحَمَّدِ بْنِ الْحُسَيْنِ عَنْ أَحْمَدَ بْنِ مُحَمَّدِ بْنِ أَبِي نَصْرٍ عَنْ دَاوُدَ بْنِ سِرْحَانَ عَنْ أَبِي عَبْدِ اللَّهِ ع قَالَ قَالَ رَسُولُ اللَّهِ ص إِذَا رَأَيْتُمْ أَهْلَ الرَّيْبِ وَ الْبِدَعِ مِنْ بَعْدِي فَأَظْهِرُوا الْبَرَاءَةَ مِنْهُمْ وَ أَكْثِرُوا مِنْ سَبِّهِمْ وَ الْقَوْلَ فِيهِمْ وَ الْوَقِيعَةَ وَ بَاهِتُوهُمْ كَيْلَا يَطْمَعُوا فِي الْفَسَادِ فِي الْإِسْلَامِ وَ يَحْذَرَهُمُ النَّاسُ وَ لَا يَتَعَلَّمُوا مِنْ بِدَعِهِمْ يَكْتُبِ اللَّهُ لَكُمْ بِذَلِكَ الْحَسَنَاتِ وَ يَرْفَعْ لَكُمْ بِهِ الدَّرَجَاتِ فِي الْآخِرَةِ
[Al-Kafi] Muhammad b. Yahya from Muhammad b. Al-Hussein from Ahmad b. Muhammad b. Abi Nasr from Dawud b. Sirhan from Abi Abdillah who said: the Messenger of Allah said: ‘if you see the people of doubt and innovation after me – then – disassociate from them openly, and increase in insulting them and speaking [negatively] about them and slandering (back-biting) them and accusing (defaming) them – so that they do not feel hopeful in [spreading] corruption in Islam, and the people become warned of them, and they [the people] do not learn from their innovations, Allah shall write for you by that the good deeds and raise you by that in stations in the hereafter. [Al-Kafi by Al-Kulayni vol. 2, ch. 159 ‘Sitting/Associating with Sinful People’, pg. 375, hadith #4, authenticated by Al-Majlisi as a Sahih hadith in his ‘Mir’at Al-‘Uqul, vol. 11, pg. 77.Numerous other Shia scholars have authenticated it too such as: ‘Ayatollah’ Al-Khoie in his Misbah Al-Fuqaha, vol. 1, pg. 354, ‘Ayatollah’ Javad Tabrizi in his Al-Irshad and many others]
What Shia scholars say
Now here the shocking thing (besides the fact that over a dozen top ranking Shia scholars have authenticated the above narration!):
The very same ‘Shaykh Al-Islam’ of Twelverism (Majlisi the palace and court Mufti of the Safavids) who authenticated the narration tried to water it down (even to a vile and vicious individual the content must have been shocking …) to the best of his ability, yet even he (i.e. Al-Majlisi) couldn’t but confess that the text does support the command to lie and level false accusation against anybody the Twelver Shias regard as an innovator!
الظاهر أن المراد بالمباهتة إلزامهم بالحجج القاطعة ، وجعلهم متحيرين لا يحيرون جوابا كما قال تعالى : ” فبهت الذي كفر ” ( 1 ) ويحتمل أن يكون من البهتان للمصلحة فان كثيرا من المساوي يعدها أكثر الناس محاسن خصوصا العقائد الباطلة ، والاول أظهر قال الجوهري بهته بهتا أخذه بغتة وبهت الرجل بالكسر إذا دهش وتحير – مرآة العقول، ج11، ص: 80
‘And what is evident is that: what is meant by “mubahita” is to impose (bind) them by (with) irrefutable proofs (arguments), and cause them to remain confused and perplexed, hesitant to produce a reply, as Allah the Elevated had said: “so the disbeliever was confounded” (2:258) [فبهت الذي كفر], and it is possible to interpret it as false accusation for a common benefit – for a lot of defective evils are deemed by the masses to be good, especially in regards false beliefs; but the former is more evident, Al-Jauhari says: بهته بهتا he took him by surprise (astonished him). And the the man was بهت with a kasra – if he is staggered and dazed.’ [Mir’at Al-‘Uqul, vol. 11, pg. 80, by Al-Majlisi]
As you can see, although he tried to water it down, yet he kept the door open for any Shi’ite to lie upon his opponent, to accuse him of falsehood, all for the sake of a ‘common benefit’.
Other Shia scholars were more honest than Al-Majlisi and admitted that the hadith constitutes clear proof for Shias to lie upon and defame their opponents with whatever they wish!
‘Ayatollah’ Ansari and ‘Ayatollah’ Rouhani (both Iran/Qom based) commented on the hadith:
‘The words “Bahituhum kay la Yatma’u” in the hadith means accusing them (i.e. opponents of the Shia) of things and assuming that they have ill intentions which is prohibited in the case of dealing with a believer; so one cannot say about the believer things like: “He might be a disbeliever or a fornicator” … And it could be left to its apparent and therefore it would be permissible to lie upon them (i.e. Shia opponents) for a certain benefit.” [Kitab Al-Makasib by al-Ansari 2/118 and Minhaj Al-Fuqaha 2/228]
The top Shia authority and hadithists of the 20th century and teacher of ‘Ayatollah ‘Ali Sistani, ‘Ayatollah’ Abu Al-Qasim Al-Khoie also authenticated the narration and says:
سؤال 1245: هل يجوز الكذب على المبدع أو مروج الضلال في مقام الاحتجاج عليه إذا كان الكذب يدحض حجته ويبطل دعاويه الباطلة؟ الخوئي: إذا توقف رد باطله عليه جاز.
Question: Is it permissible to lie upon the innovator or (person) who spreads misguidance when raising proofs against him, if the lie refutes his proofs and nullifies his claims of falsehood?
Answer: If the reply (i.e. lie) to him makes him stop his falsehood, it is permissible.
Source: al-Khoie, Sirat Al-Najah, ed. Moosa Mufid Al-Deen ‘Asl Al-‘Aalimi, 3 vols, (Iran, Qom: Maktab Nashr Al-Muntakhab, 1st ed., 1416), vol. 1, pg. 557, question # 1245
Al-Khoie also says:
أقول : قد دلّت الروايات المتظافرة على جواز سبّ المبدع في الدين ووجوب البراءة منه واتّهامه(3)، ولكن الظاهر أنه لا وجه لجعله من المستثنيات باستقلاله فإنّه إن كان المراد به المبدع في الأحكام الشرعية فهو متجاهر بالفسق ،
I say: a number of narrations have indicated the permissibility of abusing the innovator in the religion and the obligatoriness of disassociating from him and falsely accusing him, but what is evident is that there is no reason to separate this category under its own heading, for if it is meant by it an innovator in the rulings of the law then he is an open sinner fasiq … [
A similar (although the backbiting/false accusation part is watered down and the focus is more on insulting Shia opponents!) fatwa by ‘Ayatollah’ Sadiq Shirazi:
What do you say about the other places where lying is allowed, even according to Sunnis? For example, lying to rebuild ties between two people, lying to your enemies during war, lying to your spouse in certain cases etc.
This is a tpycical ‘analogy with a difference’ (qiyas ma’a Al-fariq), which treats two different things (lying in a dire situation vs lying in a theological dispute) on the same footing, and therefore invalid.
In those over cases, it is hardly likely to rebound in your face in the same way as lying against opponents in a theological dispute.
In all the other cases you listed, it is clear in what circumstances you would lie, and what the motive would be. There is also not likely to be any comeback in the event of being caught out.
After all of this, it is not wonder that throughout history, the extremist Shias (Rafidah) have been described as the most lying of all sects, in fact most lying of all creation:
الإمام الشافعي رحمه الله
لم أر أحداً من أهل الأهواء أشهد بالزور من الرافضة! – الخطيب في الكفاية والسوطي.
Imam Al-Shafi’i – may Allah have mercy upon him – said: ‘I have not seen amongst the heretics a people more famous for falsehood than the Rafidah.'[narrated by Al-Khatib Al-Baghdadi/Al-Kifayah]
And ironically we find sahih Shia narrations (pretty unknown to most Shias for a reason …) where the Imams of the Ahl Al-Bayt explicitly stated that Shi’ism (Tashayyu’) is often employed by excessive liars:
علي بن إبراهيم، عن أبيه، عن ابن أبي عمير، عن هشام بن سالم قال: قال أبو عبد الله (عليه السلام): إن ممن ينتحل هذا الامر التشيع ليكذب حتى أن الشيطان ليحتاج إلى كذبه
Ja’far Al-Sadiq said: ‘The one who adopts this issue (i.e. Shi’ism/Tashayyu’) lies until even satan relies upon his lie. [Raudah min Al-Kafi, pg. 212; Majlisi said the hadith is hassan/authentic and Bahbudi said it is sahih]
True words of Imam Ja’far Al-Sadiq that found its way in their books full of lies attributed to him. He and his grandfather (peace and blessings be upon him) are certainly innocent of such a vile belief that teaches others to lie and defame their opponents, truth-seeking Shias should asked themselves how such a criminal advice could ever have been suggested by the Prophet (peace and blessings be upon him), particularly given the emphasis placed on his own truthfulness and the Qur’anic injunctions on debating others, as well as presenting proof for your arguments.
Invite to the way of your Lord with wisdom and good instruction, and argue with them in a way that is best. Indeed, your Lord is most knowing of who has strayed from His way, and He is most knowing of who is [rightly] guided. [16:125]
Does this sound compatible with using foul language and making up lies? How many of these lies have been leveled against the Companions of the Final Messenger of God (peace and blessings be upon him) and the scholars of Ahl Al-Sunnah (Sunnis), only Allah knows, but one thing is for sure, it is fine for religious Shias who take their religion seriously to lie upon and defame their opponents, may Allah guide them and us to the truth.