You have every right to block Mark. Could you possibly send him a text before you do so explaining your reason why? I just know that if I were in his situation, I'd like some sort of explanation instead of someone just disappearing on me. But it is ultimately your decision.

I do understand Mark's point of view in that he believes he is literally trying to save your life. If I believed that a friend of mine was going to burn in Hell forever, I would do everything possible to try to save that person. However, I don't believe that this is really the case, so I don't feel obligated to impose my beliefs on other people. Mark is trying to help you, but his is misguided. You have every right to explore your personal beliefs.