Although some people hate being criticized, it seems like others are up for the opportunity to use an outside perspective. I really appreciate these people. Especially when they are experts in their domain, allowing outside opinion or being publicly open to schooling takes guts.
Additionally, it adds confidence to the group. When people are willing to take the truth, more truth can be spread around. As long as it stays mild, this confidence grows quickly to become efficiency. No more beating around the bush, just flat out tell the guy that respectfully, his idea sucks.