Ought everyone to believe there is a God?

Answer

Everyone ought to believe there is a God (); and it is their great sin and folly who do not ().

Read the 2 proof texts (KJV)

Hebrews 11:6: But without faith [it is] impossible to please [him]: for he that cometh to God must believe that he is, and [that] he is a rewarder of them that diligently seek him.
Psalm 14:1: The fool hath said in his heart, [There is] no God. They are corrupt, they have done abominable works, [there is] none that doeth good.