This is interesting phrasing. It was an often-repeated statement during American history that, "it's better 100 guilty people should escape than that one innocent person should suffer."
Prosecutorial immunity removes State consequences for violating citizen rights. Lawsuits against the officers/prosecutors/states are some of the lowest consequences we could impose; as another commenter has mentioned often they just result in the State paying out money and little to no individual consequences for bad actors. But even that is at least some discouragement against violating Constitutional rights.
John Adams commented on this by saying, "It is of more importance to the community that innocence should be protected, than it is, that guilt should be punished; for guilt and crimes are so frequent in this world, that all of them cannot be punished....when innocence itself, is brought to the bar and condemned, especially to die, the subject will exclaim, 'it is immaterial to me whether I behave well or ill, for virtue itself is no security.' And if such a sentiment as this were to take hold in the mind of the subject that would be the end of all security whatsoever."
He argued that without strong protections from the State for people's rights, that people would stop depending on or trusting the State to secure their rights, and that society would start to slip into extralegal chaos. Citizens would stop looking to the law as a protective force, and instead consider it to be something to avoid and subvert since "virtue itself is no security."
This is a particularly prescient idea today. We tell people to trust the legal system to protect their rights. But prosecutorial immunity undermines that message, because people see that their rights can be violated by the State itself and they will have no legal recourse to fix the situation. When they see that, we run the risk of making them disregard the entire legal system. Why cooperate with the State at all in any capacity; why trust the process when the process doesn't hold itself accountable to its own standards?
We live in a system with double standards, where citizens can be prosecuted, penalized, and even jailed for lying to the police or the FBI under extremely broad criteria, but where prosecutors and the State suffer no personal penalty for withholding evidence from the defense during a trial. How much damage does this do to our institutions? How can we possibly hope to convince ordinary people that an institution with those standards is trustworthy?