If they really don’t believe then why?

If I were to react with extreme anger, personally attack, belittle, or threaten a person because they openly choose to believe in and worship the tooth fairy wouldn’t my reaction be considered  silly and uncalled for? After all, maybe they are crazy or simply misinformed to believe such a lie.  If they told me why they believe and attempted to get me to believe also should I be threatened or take them serious?  Of course not.  This  makes me wonder about people that say they do not believe in God. If they do not believe that God exists then why should the mere mention of what they consider a myth or lie cause such strong reactions? If, in truth, they do not believe then their extreme response is irrational to say the very least.