Why do Christians get angry when one states that they don't keep the law or the old covenant when they don't?

If anything, the Sermon on the Mount strengthen and reiterated the commandments. The laws were never invalidated until the Roman Church decided to release the "Christians" from the Jewish Law. Another extension of the fabrication of a new religion which drew upon its' pagan roots with validation from Jewish tradition. If there is a new covenant, it is with Rome and her followers. It has nothing to do with The Hebrews or their God.