"Radical KKKer's would not effect Christianity, because Christianity is based on the commands and example of Christ."
The KKK profoundly effected Christianity and American society.
The Klan was able to infiltrate and control many of the largest American denominations. Most segregated their institutions or banned African-Americans, outright. Some promoted Klan recruiting in their ranks. Most supported oppressive Jim Crow Laws in the South. Even in the early 60's while major American denominations denounced racism and bigotry, they refused to integrate.
The Klan was responsible for the propaganda film, Birth of a Nation, which premiered at the White House (it was orginally called, The Clansman). It was the highest grossing film of its day.
The Klan controled Southern politics through their political arm, the Democrat Party. The Klan built memorials to the Confederacy and its leaders throughout the South.
It took the US government to detangle the Klan's tentacles from American society. Thankfully, we have turned the page.