Jesus Endorses The Old Testament In Toto

Do not think that I have come to abolish the Law or the Prophets; I have not come to abolish them but to fulfill them. I tell you the truth, until heaven and earth disappear, not the smallest letter, not the least stroke of a pen, will by any means disappear from the Law [the Old Testament] until everything is accomplished. (Matthew 5:17-18)

I've asked a few learned theologians about this... never a clear enough answer as to why this doesn't condone a whole lotta murder and slavery and rape and other stuff...