There is more to being a Christian than just carrying the name around. Jesus tells a couple of parables that deals with this very question.
Some people are like seed along the path, where the word is sown.
As soon as they hear it, Satan comes and takes away the word that was sown in them. Others, like seed sown on rocky places, hear the word and at once receive it with joy. But since they have no root, they last only a short time. When trouble or persecution comes because of the word, they quickly fall away. I will show you what he is like who comes to me and hears my words and puts them into practice.