If we believe we have a free will, we are stuck in a cycle of thinking that we are choosing things independently of prior causes. This may cause us to ignore the causes of what is happening. If instead we notice that a person continually does the same things, this suggests there is a reason for it.
If someone continually does actions that we consider good, we may think of them as a good person. If they do what we consider bad, we may label them as a bad person. But when we have gone that far, we must ask ourselves, if this person was freely choosing their actions every day, why are they so repetitive? Because we notice a pattern, we may still unconsciously label them as good or bad. This is automatic because it helps us avoid those we consider dangerous, but we must become conscious about it if we expect to be able to avoid the danger.
While free will belief does prolong ignorance, I do not think that we can remain ignorant forever. Looking at what people have done in the past is a good guide to predicting what they will do in the future. We constantly label people as pro-life, pro-choice, christian, atheist, democrat, republican, determinist, or libertarian. These labels may not be accurate but they do often determine who we spend time with, who we vote for, what books we read, and which lives we attempt to save. The relevance of this is something we cannot ignore forever.