There's a difference between atheism and "anti-christ." Anti-christ suggests that the material is actively attempting to discredit christianity. I am in no way a christian, but passing out stuff or promoting that actively puts down another religion (as "Anti-Christ" would suggest) shouldn't be allowed. Anything actively assaulting a religion is also assaulting those people who believe in it, which is the same as being prejudice against them based on their beliefs. Wearing a shirt that says "I'm an Atheist," well, that's what you believe, and that's fine. You aren't forcing it on anyone, and although someone may disagree with you, no one is hurt by the statement. But if you wore a t-shirt or brought a pencil to school that said "CHRISTIANITY IS A LIE," I can see why teachers may want to dispose of that stuff - it's offensive to people who are christians, as you are discrediting something they believe in. They have every right to believe in christianity if they so desire, just as you have a right to be an Atheist if you desire.