I think it is only a problem if the fear turns into aggression, and especially uncontrollable aggression. Perhaps the dog was previously abused and so may exhibit some fear or cowering around individuals that are similar in appearance to the person who did the abusing. I think these types of issues can be dealt with. I don't remember what you wrote in the other post-but if he is showing some fear around certain individuals, I have heard that having those people give her a yummy treat or something can help him to overcome that fear.