There are lots of possibilities: I can be willfully ignorant of a. the principles of justice and/or b. the context in which I judge/act, so that I am morally responsible for the consequences of my actions; I can be blissfully ignorant of both and therefore less culpable (though still causally implicated); I can be ignorant of my participation in/propagation of structural injustices while successfully avoiding interpersonal injustice; I can in fully knowledge act unjustly as a consequentialist means to some greater end; and so on. Do you have a specific scenario in mind?
I try to imagine a scenario, where the basic structure of society is fundamentally unjust because of false ideological, religious, scientific, or cultural reasons. As such, most of the citizens acquire a sense of injustice by ignorantly legitimizing falsehood.
I guess an obvious example of that, from a Marxian political economic perspective, is the false common conception of the wage relation as a fair exchange between equals, perpetuating the structural injustice of widespread exploitation.
What an excellent and meaty question!! I would say that ignorance is part of the problem but injustice is built into organizational systems and become institutional racism. I believe the addressing ignorance is the first step in addressing the biases.
I don't believe in the root cause. Sure, people can be prejudiced and unjust because of ignorance. But I think greed, obsession with power, tribalism, and kinship can also be major causal factors, and one can be knowingly prejudiced or unjust in accordance with such factors.
Also, I think a distinction needs to be made between prejudice and prejudging -- the two are often conflated. Sometimes a quick judgement or a prudential judgement needs to be made on less than optimal evidence; that is prejudgement but not necessarily prejudice. For example, a woman walking alone at night down a dark street might be wise to avoid coming near to a man approaching from the distance. She would be forming a prejudgement based on reasonable caution and common sense, not prejudice toward men.
No, I wouldn’t say ignorance is the root of prejudice. Prejudice can be a learned outcome, but also throughout history some groups had tension with other groups, hence developing prejudice.
Although ignorance/misconception might have caused great injustice historically (witch trials for instance), I don't think today's injustice can be put on ignorance.
Today's greatest injustices are arguably related to the crazy inequalities in access to material resources. More than 5000 children dies daily of starvation. These death could easily be avoided economically speaking and yet the situation continue. Ignorance can't be blamed for this injustice. Quite oppositely the injustice is perpetuated despite being well recognized.
Today's greatest injustice as such are perpetuated purposefully. The purpose of this perpetuation is to maintain the dominant class in power.