Regarding the hadith: “Speak of the good of your deceased and abstain from speaking about his wrongs...”
The commentators explain here that in certain circumstances it will be permissible to mention the wrongs of the deceased if there is fear of Fitnah by remaining silent on his wrongs. They cite the examples of a Faasiq and a Bid'ati and a few others.
Hazrat Moulana Ganghohi Rahimahulla has explained this very beautifully in Kawkabud Durri. 
If this Hadith is general that you cannot speak out of any person who passed away then you cannot speak out against Hajaaj. Why did the Sahaabah and Taabi’een speak out against him after his demise.
Similarly, why did the Muhadditheen write kitaabs on jarah wa tadeel, explaining the wrongs of the various narrators of Hadith. All written after their demise for the benefit of the ummah, to save them from accepting Ahaadith from wrong people.
Ulama learn about criticisms levelled against Moudoodi and even ibn Taymiyyah.
Are they implying that all that they learnt on these subjects and ghair Muqallids based on these people who have passed away is also incorrect and that our Akaabireen have erred?
Those who take up issue with refutations and critiques against Ulama who have passed away recently should study the subject matter further. We refer to Ulama as well.
(A more detailed article on this is being prepared and will be published soon, Insha Allah Ta'Aala)