Before Hacker School, I never realized how unhelpful this was. The naive logic is, "well, I'm genuinely surprised that this person didn't know this". But in the grand reality of things, all of us know very little. Even experts in one area, don't know basic things in another area. By removing the shaming of admitting what you don't know, Hacker School encourages everyone to move past that and help each other learn.
I think this is exactly why they added this rule: some people didn't realize the negative effects of acting surprised when someone doesn't know something. The jerks are probably still going to be jerks of course, but for the others it's a chance to learn about how to better interact with the people around them.
