Why do atheists have to be anti-Christian? If they don’t believe in God, what difference does it make to them what others believe?
Christ represents the SCARIEST scenario of all: He is real. He is the Way, the Truth and the Life.
They are also angry with Him because, I suspect, that God didn't give them what they wanted or took someone away from them or let someone loved suffer. So, they pretend He doesn't exist. That's their punishment of God ... nonbelief.
Athiests remind me forcibly of spoiled, thwarted 3-year-old termagants.