This is a misperception. Sermon on the Mount has nothing to do with morality; it is simply an observation on the nature of reality.

In fact, New Testament has only a few obvious things to say about morality – eg that it is good to help sick and accident victims.

On the other hand it consistently condemns moral rules.

http://kingjbible.com/luke/11.htm

Luke 11:37-52
“37 And as he spake, a certain Pharisee besought him to dine with him: and he went in, and sat down to meat. 38And when the Pharisee saw it, he marvelled that he had not first washed before dinner. 39And the Lord said unto him, Now do ye Pharisees make clean the outside of the cup and the platter; but your inward part is full of ravening and wickedness. 40Ye fools, did not he that made that which is without make that which is within also? 41But rather give alms of such things as ye have; and, behold, all things are clean unto you.

42But woe unto you, Pharisees! for ye tithe mint and rue and all manner of herbs, and pass over judgment and the love of God: these ought ye to have done, and not to leave the other undone. 43Woe unto you, Pharisees! for ye love the uppermost seats in the synagogues, and greetings in the markets. 44Woe unto you, scribes and Pharisees, hypocrites! for ye are as graves which appear not, and the men that walk over them are not aware of them.

45Then answered one of the lawyers, and said unto him, Master, thus saying thou reproachest us also. 46And he said, Woe unto you also, ye lawyers! for ye lade men with burdens grievous to be borne, and ye yourselves touch not the burdens with one of your fingers. 47Woe unto you! for ye build the sepulchres of the prophets, and your fathers killed them. 48Truly ye bear witness that ye allow the deeds of your fathers: for they indeed killed them, and ye build their sepulchres. 49Therefore also said the wisdom of God, I will send them prophets and apostles, and some of them they shall slay and persecute: 50That the blood of all the prophets, which was shed from the foundation of the world, may be required of this generation; 51From the blood of Abel unto the blood of Zacharias, which perished between the altar and the temple: verily I say unto you, It shall be required of this generation. 52Woe unto you, lawyers! for ye have taken away the key of knowledge: ye entered not in yourselves, and them that were entering in ye hindered.”