How can anyone believe in Honor Killings?

I have been reading up on the practices of "honor killing" in foreign countries. It is appalling. I would like to know if anyone beleive people should be doing this crap? I have read stories that somebody's own parents and siblings and murder their own daughters because she "dis-repsected" the family. Unbelievable. Now, I do not believe it be a total religious thing. The Koran never mentions it. But, the radical Muslims DO practice it. Sad...sad.