It strikes me, and should you too, that someone would complain that an eyewitness believes what they saw. I mean, if I saw a car crash take place, should my testimony be discredited because I am biased towards its taking place? No. The reason is because my bias has a foundation. If I saw an event and refused to believe that it took place, I would be in denial of reality. And everyone should reject my testimony because of my denial of what I saw, in favor of those who accept what they saw.
But let's just say that I go along with the idea that founded bias (eyewitness testimony in this case) is still not to be trusted. If eyewitnesses cannot be trusted due to their bias, then we must reject any and all records of science and history that were recorded by eyewitnesses. We could only accept those who were not present to record what actually took place. Those who are not eye-witnesses can knowingly or unknowingly produce works of fiction. Frankly, they can't know whether they are producing fiction or not because their sources (which do eventually come down to eye-witnesses) cannot be trusted. Ironically, works of fiction are favored as works of truth over works that record what actually took place.
The ironic thing here is that many people believe the Bible to be a work of fiction. If they also wish to reject the eyewitness testimony of the Apostles based on their bias, they must accept the truth of the Bible based on the fact that it records fiction.
As illogical as that conclusion sounds, it is exactly where the logic leads if someone is to reject eyewitness testimony due to bias. However, the reason why the conclusion sounds illogical is because it is illogical. But the reasoning doesn't fail anywhere that I have presented here, it fails in the conclusion that eyewitness testimony should be rejected because the witness is biased. When we correct this flaw in our reasoning, we see that the fact that the Apostles were eyewitnesses to the life, death, and resurrected Jesus is an extremely compelling reason to understand that Christianity is true.
There is nothing wrong with maintaining a bias based on evidence. That is what a belief is. If we believe something to accurately reflect reality, then we tend to be biased towards it. The kind of bias that is not good, is a bias that goes against the evidence. For more on this "can of worms", please see the following posts:
What's Important About Consistency?
Consistency Among Disciplines
Nature vs. Scripture
I also recommend the book "Cold Case Christianity" by J. Warner Wallace for more on eyewitness testimony.