People will chose to believe that which they want to believe. Most often, that which agrees with their lifestyle.
Are there "differences" between the OT and NT. Sure. But the Bible has endured thousands of years of tinkering, starting with the Jews and then the "Christian" church.
But, the idea that God was ruthless in the OT and snugly bugly in the NT is preposterous.
God is Love. But Love demands justice. How would God be showing love to the fatherless boy if he coddled the bastard who beat him?
In the NT, Peter started a community. That community was communist in the true sense. In came a couple of capitalists, Anninias and Saphira. They were busted for practicing capitalism in the heart of Gods community. God struck them dead. The Christian God of the NT, the God of love, struck them dead.
And they deserved it. That's what Love demands.
Jesus preached the God of the OT, as did Paul. But their teachings clarified much that was obscured by the Jews.
But people will convince themselves of whatever... here no different than in dubland past.