The "No True Scotsman" defense is a logical fallacy and a very weak argument because it dismisses a Christian's immoral behavior by claiming the person was never a "real Christian" in the first place. Now that I am no longer a Christian, I refuse to be lectured about "sin" by Christians, who are just as guilty as anyone else for disobeying the biblical commandments. Christians are not more moral than people who are not Christians, despite what most Christians seem to think. In fact, most Christians behave exactly the same as the non-Christians they pompously judge and lecture about "sinning against God."
Christians, like everyone else, lie, steal, covet, lust, commit adultery, commit crimes, divorce, and remarry. They have a reputation for being rude and obnoxious to people they dislike, such as other Christians who attend a different church, people who practice another religion or aren't religious, and people who hold opposing political views. Furthermore, many Christians clearly harbor personal prejudices against people they dislike, such as LGBTQ+ people and, in some cases, undocumented immigrants. Also, many Christians continue to oppose LGBTQ+ equality as well as a woman's right to control her own body concerning pregnancy. Finally, Christians have a history of deliberately discriminating against people based on their sexual orientation.