Sin is so serious that Jesus came to die on the cross. Although Jesus came and died for the sins of the world, during His earthly ministry, He never called anyone a sinner! That is a profound demonstration of love and a choice of word to the people He came to die for.
I wish I am like Jesus in my choice of words when talking to people who do not know God. I wish I could love like Jesus did. I have a problem when my fellow preachers have yell to their audience, "You are sinners!"