Because once you accept you are susceptible to a bias, and you know that a person fits that bias, -what do you do-? You can ask "if this person was (not this bias) what would I do", but -can you be sure-? Do you have an exactly equivalent data point to compare against? Of course not; everyone is a bit unique. Can you be certain, if you pass on the person, it was due solely to the heuristics you've built up around resume and etc, and not you reinterpreting them through your bias? Can you be certain, if you hire a person, it was solely due to the heuristics you've built up around resume and etc, and not you overcompensating to try and account for your bias?

It's going to influence you. It -may- not change the outcome, but if you aren't concerned about that, no matter what steps you take, then you're deluding yourself.