First of all, a court of law does not get to decide what is objective fact or not.
Secondly, there is a huge amount of evidence to show that testimony is unreliable. Here are just a handful of sources...
Memories are treated as essentially “flash-bulb” photographs that never change after they are recorded, no matter how often the witness recounts the memory, despite the well-established and accepted body of scientific literature demonstrating that this is not true.
“How the Science of Memory Can Be Used in Fact Witness Questioning” - Lexology
New events can be added and we can change what we think we remember about past events, resulting in inaccuracies and distortions.
Eyewitness Testimony and Memory Construction | Introduction to Psychology
One factor consistently identified as problematic is erroneous eyewitness testimony or identification, which is found to be a factor in over two-thirds of the documented cases of wrongful conviction in the United States. Commentators, courts, and others have offered several approaches to the problem of faulty eyewitness identifications, ranging from the exclusion of questionable eyewitness testimony altogether to the prohibition of any conviction based solely on uncorroborated eyewitness testimony.
https://digitalcommons.law.yale.edu...psredir=1&article=1028&context=student_papers
Many researchers have created false memories in normal individuals; what is more, many of these subjects are certain that the memories are real.
Why Science Tells Us Not to Rely on Eyewitness Accounts
Eyewitness testimony is unreliable because of the science of how we see.
The utter unreliability of eyewitness testimony
A person's ability to identify another person depends on his capacity to perceive, remember, and articulate what occurs before him. That the processes of perception, memory, and articulation are subject to defects which might affect the reliability of eyewitness evidence has become a focal point for analysis and psychological research.
https://core.ac.uk/download/pdf/235287698.pdf
Memory is not as reliable as we would like to think. In fact, it’s easy manipulated whether intentionally and unintentionally.
https://www.toronto-criminal-lawyer.co/witness-testimony-unreliable/
...one of the greatest misconceptions we continue to have about memory is that it is largely an accurate recorder, faithfully transposing into our brain events as they occur. From a witness’ point of view, it is important to remember that whilst we often doubt the memories of others, we rarely question our own. However, all witnesses, no matter how seemingly reliable and honest, are accessing changing or changeable data. The process of experiencing or acquiring, laying down or storing memory and then reproducing an account, all of which is involved in “recalling or “remembering”, and therefore giving evidence in a criminal trial, is disconcertingly malleable. It is at best, almost always, a rough reconstruction with inaccuracies and distortions.
https://www.legalaid.nsw.gov.au/__d...to-you-problems-with-eyewitness-testimony.pdf
Social scientists have demonstrated through studies since the 1960s that there was significant reason to be concerned about the accuracy of the eyewitness-identification testimony used in criminal trials. Although witnesses can often be very confident that their memory is accurate when identifying a suspect, the malleable nature of human memory and visual perception makes eyewitness testimony one of the most unreliable forms of evidence.
https://www.ncsc.org/trends/monthly...ss-identification-testimony-in-criminal-cases
Eyewitness testimony is more fallible than many people assume. The advent of DNA analysis in the late 1980s revolutionized forensic science, providing an unprecedented level of accuracy about the identity of actual perpetrators versus innocent people falsely accused of crime.
https://www.psychologicalscience.or...s-testimony-is-the-best-kind-of-evidence.html
Eyewitness identifications play an important role in the investigation and prosecution of crimes, but it is well known that eyewitnesses make mistakes, often with serious consequences.
https://www.pnas.org/content/114/30/7758
And these are all from just the first page of a Google search result. Human memory is notoriously unreliable, no matter what claims you make to the contrary.