Christianism begins with a false premise and a wrong accusation:
"He[Jesus] is the atoning sacrifice for our sins, and not only for ours but also for the sins of the whole world."
(1 John 2:2)
"Who is the liar? It is whoever denies that Jesus is the Christ."
(1 John 2:22)
So, Christianism tells us that whoever denies the role of Jesus as the Christ, that one is a liar. This premise is already immoral.