Jesus warned that “out of the heart come wicked reasonings, murders, adulteries, fornications,?

True. The Bible tells us that "the heart is treacherous, who can really know it." Jeremiah 17:9

And left to our own devises, we fail miserably...even though we have the best intentions, mankind is dealing with imperfect flesh and we need to be instructed by God in his ways and standards to become successful in pleasing Him and helping others to come to an accurate knowledge of Him and gain salvation through the sacrifice of Christ.

http://www.jw.org/en

Matthew 5:8

Blessed are the pure in heart, for they shall see God.

To be pure in heart is to be single in purpose, to have the single goal of accomplishing God's will for God's glory (1 Cor. 10:31).

This is for the kingdom of the heavens. Our spirit is the organ by which we receive Christ (John 1:12; 3:6), whereas our heart is the ground where Christ as the seed of life grows (13:19). For the kingdom of the heavens we need to be poor in spirit, empty in our spirit, that we may receive Christ. Also, we need to be pure, single, in our heart that Christ may grow in us without frustration.

I agree. This is why man can't save himself. Our hearts are desperately wicked. We need to be given new hearts.

Well if you believe the first testament then its slabery, stoning and mass murder (all ok)

I disagree with the "reasonings", for it is not reason, but foolishness.