To them, the cross is like a mirror, and their reflection horrifies them. They'd rather not look at it.
Today, the atheists fear of Christian icons is nothing short of irrational. They seem to either tremble in fear, or lash out with rage. (Deep inside, they know they have but little time. Demons always screech the loudest when they're being cast out.)
Your insight is spot on. Thanks for sharing it with us.