It is quite another thing to succumb to Delusion.   Delusion is the sad State a person enters when he begins to accept a source of Information without consideration of its truthfulness and motives.   

Delusion is a False Reality constructed on Ideas or Opinions - Not facts.   Actually, Facts are the Enemy of a person who is Delusional.   

When a person is Delusional they may come across as confident in their beliefs.   However, this is Just bravado.   In Reality their Beliefs are shallow and fragile.   

The Only Way to bring someone out of Delusion is by Revelation - Revelation of something which conflicts with their Belief System is True.   

Arguing with a Delusional person causes them to hunker down in their Belief System.   The best Way to Help someone out of Delusion is to Ask them questions leading them to See a conflict in their Belief system.   

The most important thing You can share with an Unbeliever is that Jesus Loves them and that He wants a Relationship with them.   This is hard to resist because it is the Truth and it Speaks to an inherent Need in man to be loved and to have a Relationship with his Creator.   

If You Know a person who has Not Received Jesus Christ as Lord and Savior that person is Deluded.   They are Lost.   You may be the Only person to ever share with them the Truth.