A typical response to this accusation is that Latter-day Saints do not teach a different Gospel than was preached by the ancient apostIes--it is the various Christian sects who do. But this response is incomplete because the original question is based on an erroneous understanding of Galations 1:6-9. We should examine this scripture closely and determine who was writing to whom, when, and why.
Paul was writing to the Galatians to warn them about what he perceived as a growing problem within the Church itself. People had entered his flock, attempting to mislead it by preaching another gospel, a perverted one, different from the one that Paul himself had preached to these Gentiles who had just joined the Church.
Who were these people? Were these pagans or some other brand of non-Christians preaching a perverted gospel? It was neither. In fact, they were fellow Christians from the Church at Jerusalem who were trying to solve what they saw as a growing problem among the non Jewish converts. The brethren from Jerusalem wanted all male converts, Jewish and Gentiles alike, to comply with the requirement of circumcision and to make a commitment to keep the Law of Moses.
Earlier, Paul had been upset when Peter entered Paul's mission field teaching "another gospel" -- a gospel of circumcision, while Paul advocated the gospel of uncircumcision (Gal. 2:7). It was Peter who received the vision to widen the ministry to all people, including the Gentiles. This was a marked change from the ministry of Christ, who took his message only to the House of Israel. Yet Peter still wasn't convinced, as evidenced in Galatians 2, that there should be full fellowship with the uncircumcised Christians. Paul therefore referred to what Peter was teaching as another gospeI--the gospel of circumcision.
Students of the Bible know that circumcision was a divisive issue in the New Testament church for many years, even after Peter's vision of the "unclean" animals when he was told "what God hath cleansed, that call not thou common" (Acts 10:15-35). This controversy over the gospel of circumcision (Gal. 2:7) caused so much of a disruption in the church that the Apostles once gathered in Jerusalem to resolve the issue and to determine and write their unified position (Acts 15).
But back to Galatians--Paul was upset with Peter, who had been dining with the Gentile Christians until some of the Jewish Christians came into the area. Peter then separated himself from the Gentiles, which was so upsetting to Paul that he "withstood him to the face," or in other words, discussed it openly with Peter at Antioch (Gal. 2:11).
Paul continued to be angered by Peter and certain others who were still preaching the gospel of circumcision to the uncircumcised Gentile Christians. Noted Christian theologian F. F. Bruce adds his comments on the issue Paul was addressing in Galatians chapters 1 and 2:
If God's redeeming grace was to be received by faith, and not by conformity with the Law of Moses, then it was available on equal terms to Jew and Gentile and to make a distinction in practice between Jewish and Gentile believers, as Peter and the others were doing, was in practice to deny the gospel (Paul: Apostle of the Heart Set Free, p.178).Galatians 1:6-9 has to do with a specific doctrinal problem confronting the early Christians. To apply this scripture to any other doctrine with which detractors disagree is to wrest the scriptures.