They use them to say, "See, we need to be preaching the 10 Commandments." But when you look at the context it isn't so.
"The Law and Prophets were proclaimed until John. Since that time, the good news of the kingdom of God is being preached, and everyone is forcing his way into it. It is easier for heaven and earth to disappear than for the least stroke of a pen to drop out of the Law." (Luke 16:16-17)
Let's ask a question right here...
Why is everyone forcing their way into the kingdom?
Look at the context. The Law is stiff. It does not bend. When people understand how difficult it is to keep the law they will gladly choose the alternative: The Gospel. The Good News.
Why did Jesus say that the Law and Prophets were no longer proclaimed?
Because he came to fulfill the Law. When something is fulfilled, ("It is finished.") there is no need to strive to complete it.
Finally, right before Jesus ascends to heaven, he reiterates this point. "...repentance and forgiveness of sins will be preached in his (Jesus) name to all nations..." (Luke 24:47)
Don't you think Jesus would have said, "Oh yea, start proclaiming the Law with that too," if he wanted us to proclaim the Law? He didn't, though. Preaching the Law is back-tracking. Paul backs this up again in 2 Corinthians 3 (Summarized) "Everytime Moses (Old Covenant Law) is read, a veil covers the hearts of those listening."
He is saying when the Law is read as a means of self-righteousness and is cheapened, people are blinded to the simple truth of the Gospel: God has chosen to forgive and forget our sins through Jesus Christ. (Hebrews 8:12)
When people finally do hear this simple but powerful truth, it will be the best news they will ever hear. And you will see them run to the King - Jesus.