These people are Christianphobes.
A better term is staurophobia which is an irrational fear/hatred of the Cross and especially of Him Who it represents; those who are thus afflicted are staurophobes.
(The term comes from the Greek “stauros” [cross] and “phobia” which is [an irrational fear.] I did not coin the term, another poster did but it is a good way to describe this condition.)