Why are those who reject God actually rejecting love?

Those who reject God are rejecting Love.  God is Love.

No one has ever found an error in Scripture, and those who don't want the Bible to be God's Word do so because they want to follow the leading of their own mind rather than receiving the revelation of God's will in their lives.  

They want darkness more than they want Light.

They want darkness, and they hate the pure love of God. They desire pleasure more than they love God. They want to call good "evil" and they want to call evil "good."

They need to understand that sin is falling short of the glory of God, falling short of God's glory.  Look at what they are missing.

They try to rationalize to themselves and to others that God will not see and that God will not judge. God knows that all the arguments come from a rebellious heart and He still holds out His hand for any who will turn from their rebellion and who will turn to Him.
John 3:19
2 Timothy 3
I John 4:16