The problem here is that there is a vast disjuncture between Gandhi the historical figures versus the popular mythology that has built around him. The 1982 biopic is a reflection of this latter aspect of Gandhi's image. The film presents Gandhi and his world in starkly Manichean of light versus dark. Note that Kingsley's performance (almost universally praised among critics) is one that highlights Gandhi's stoic and moral gravitas and thus accentuates this duality. Many of the other historical characters in the film shrink compared to him.
The reality is that the historical Gandhi inhabited a highly complex political world in which often belies reducing it to simple terms like good vs. evil or justice vs. injustice. That Gandhi inhabited and operated in such a world is not even an open secret, but the strength of his mythologized public image means that the act of uncovering the historical record carries far more weight to them than less valorized historical figures. For example, there have been recent publications of Nixon audio tapes that highlight his various racial, sexual, and political prejudices, often expressed in language the mods here would require a NSFW tag for, yet these revelations are somehow not as alarming as Gandhi using a formal greeting of "dear Friend" in a letter to Hitler (which the critic in the OP's first link finds appalling).
Jewaharlal Nehru actually advised David Richard Attenborough not to deify Gandhi, as "that is what we have done in India and he was to great a man to be deified." Although Attenborough claimed to follow Nehru's advice, Gandhi has fallen into the trap of many biopics by oversimplifying its subject and the context of the times.
Source
Carnes, Mark C. Past Imperfect: History According to the Movies. New York: H. Holt, 1995.
I recommend you go to his own autobiography to look at how his belief in universal human rights evolved over time, after being raised in two cultures that were perfectly happy with a rigid ethnic hierarchy. It turns out neither Gandhi, nor any of my own Catholic saints were born fully adult and fully mature.
Examples - He first became politically active and well-known while working as a lawyer in (British) South Africa. His early campaigns focused on bringing upper caste Indians to something like parity with the English. He burned little of his scarce political capital on native Africans or lower caste "coolies," at first. This evolution was only hinted at in the movie.
Critics may also go after his difficult relationship with his son Harilal Gandhi. It is above my paygrade to speculate on whose fault it was that his life unraveled as it did, but others may not hold back.
He also spends many pages of his autobiography discussing some medical quackery that he experimented with - not so much a moral failing, but fodder for pundits and cranks on the internet. He tried many fad diets with varied results. Any comments related to sex also clearly are coming from someone outside of Victorian British Western culture, so again more fodder for critics and cranks.
Related question: how come the movie gave such a negative depiction of Mohammed Ali Jinnah, despite relatively positive views from academic historians?