My opinion on this is that one is a hate group(KKK) and the other (mafia) is a criminal organization. Most mafia members will not admit they are are members.This makes it harder for law informent to prove they are members and the ones that do will only admit to it after they are caught and may use it to get a lighter sentence.
What I find puzzling is how much proof does law inforcement need for the 1% OMC that wear their patches openly; aren't they telling the world that they are members of the criminal organization.