Mainstream Islam: Sunnis, Shias, & Sufis
For example, Terrorists are not Muslim by definition, however they call themselves Muslims and because in Islam we don't have excommunication, they can keep calling themselves anything they want, but the truth of the matter is that they are not following Islam or it's teachings if they are doing terrorism. This is the one thing that is different than most Christian sects is that as a good Muslim or bad Muslim we as a community can not excommunicate them as much as we understand their hypocrisy and evil they follow. It is not for us to judge who is or is not a Muslim, that is up to God. However, we can judge to see if the person is following the Islamic teachings by their actions. If somebody is advocating hate and violence in an offensive manner and they are advocating the killing of women, children, old, unarmed, animals, trees, etc. then you know that is not Islamic. As a Muslim it is your duty to fight the hypocrites such as Al-Qaeda/Taliban etc. because they are doing evil in the name of your faith.
Here is an excellent speech by the Grand Mufti of Syria in regards to Muslim Unity and refers to the extremists that keep the Muslim Community divided:
The first thing every Sunni and Shia Muslim in America should have done when the 911 attacks happened is to declare a Holy War on the Terrorists, because it is their duty as Muslims who are American Citizens to defend their nation against all enemies...regardless if they call themselves Muslims or not. The best ally the USA has in fighting the radical elements in the Islamic World are true mainstream Muslims who are loyal to their nation. However, if American Muslims who follow the Islamic duty of loyalty to your nation are persecuted by right wing fanatics, then we as a country will eventually lose to both the Christian and Muslim fanatics foreign and/or domestic. If you are an American and believe in your nation, then don't persecute Muslims who have done nothing to you. The people who have been hurt the most worldwide are Muslims who have been the #1 victim of Al-Qaeda. This is why Muslims are the #1 force that are fighting these extremists. The same way American Christians fight their extremist groups, Muslims do the same.
Let's unite in faith and stand firm against those who wish to divide us and destroy us as a nation and as a world. Let's not allow the Islamophobes, Anti-Semetics, etc. to dictate to us what we should do! The next time an extremist tells you Shia's, Sufis, Jews, and Christians are Kaffir (Infidels)...stand up against those hypocrites and tell them "NO!" they are not. The Prophet (pbuh) was a defender of all people...Muslim or Non-Muslim even at the expense of his own well being. A Muslim must stand up for justice and allow it to flourish within society. There has to always be a voice standing against injustice.