I agree that it does not matter whether Columbus did or did not discover America. It also does not matter what people perceive. What matters is the truth as best it can be determined.
I fail to understand how you can say that 'witnesses can't be taken as reliable sources'. This would suggest that we cannot rely on any history. Although we can't always decipher the emotions and intent of historical figures, we do have fairly good evidence on their actions.
It has been fairly well proven that Leif Erickson was in North America long before Columbus. It is also accepted as fact that colonization and exploitation (not intended as a negative) did not begin until after Columbus rediscovered and promoted the New World.
What is condoned at a specific time by the greatest amount of people at that specific time, although certainly a consideration, is not a valid basis for judging the character of people living in that time. We honor the Christian martyrs of the Roman period not because they went with the norm, but because they gave their lives instead of going with the norm.
Would you not condemn the crucifixion of Jesus, even though that was condoned behavior accepted by the majority of people at that time.
I'm have no goal of tearing down Columbus. He was brave and succeeded in his mission where many, many before him had failed. But as we celebrate his success, we would do well to also reflect on his shortcomings and the shortcomings of his era.