According to the University of Chicago:
"Bias is a pre-formed negative opinion or attitude toward a group of persons who possess common characteristics, such as skin color, or cultural experiences, such as religion or national origin."
So, should we ever be biased? And if the answer is yes then should we hide our biases for signaling reasons?
Or should we take into account that many people have irrational biases against those who possess different skin colors, religions or national origins. So perhaps a high percentage of any negative biases readers of this blog have are irrational and so maybe the best course for us rationalists in training is to work against having any negative biases.
Are you asking whether it would ever be justified to
(a) hold negative opinions against a group, even if the individual group members may vary on the negative quality
or
(b) hold a negative opinion that isn't based on any evidence?
For example, being afraid of all spiders because some are poisonous would be (a), while being afraid of spiders because you believe they have mind control powers would be (b).
Assume that on average members of a group are more likely to have a negative quality than are members of the general population.