Constitutionally, specifically referring to the First Amendment, the administrator is wrong to bar Mr. Spencer from speaking on campus (you cannot prohibit a protest/rally etc. even if the message is one of hate and bigotry). The administrator can argue that the KKK is an organization that has advocated violence in the past and continues to do so today and if Mr. Spencer were to come to the campus, he may incite violence among the students. The administrator can also explain the KKK and their beliefs go directly against what the college stands for: peace, diversity, free thinking, morals/ethics, etc.