Many fallacies promoted to make Islam appear peaceful, and many Muslims believe it. But the core text of the Quran is filled with the most barbaric commands imaginable. Any of the peaceful messages are 'abrogated' or annulled by the Koran's own rules. Just read www.thereligionofpeace.com to see what I am referring to.
Like many historical texts that come from different eras of civilization and from disparate sources, there will be mixed messages and passages that can be clearly read as promoting violence. The same can be said of the Torah and the Bible as well. These documents were written at a time when violence was more ordinary.
The Koran does indeed preach violence. There are over 100 verses within the Koran that speak on going to war against others due to others being non-believers. Those verses are very graphic and are very far from being peaceful. As a matter of fact, there is little to no talk about being peaceful to those who do not follow the Koran's teaching inside of the Koran text.
Of course the Koran doesn't preach violence. In the Koran it states to not fight except for self-defense. In Islam's past there were many battles in the religion of Islam, but it was all for self-defense and for the sake of Allah and Islam. Muslims aren't supposed to go around killing random people. That is haram (a sin). We are told to be friends with people of all religions except when we are at war with them.
The verses that do talk about war against nonbelievers refers to that situation in time when Muslims were being persecuted as they were the minority and on the brink of extinction. They can NOT be used today. As Muslims accept they were reveled to the prophet to help understand how to deal with the they were in. Ultimately the Quran promotes co existence, respect for life and respect for the people of the book eg Christians, Jews, Sabians etc.
People that interpret it and use the Quran as a justification for evil are uneducated and unaware and uneducated regarding the study of the Qur'an.
When the Quran talks about war it is only in SELF DEFENSE eg of protection of property and life.
The Koran may have passages glorifying violence and war, but ultimately it is a peaceful text. It honors respect and charity, and does not look to punish as much as teach and show love. Our perceptions of the Koran are skewed by the mainstream media and extremists that use the Koran to justify terrorist acts, but in reality it does not preach the messages we so often hear.
The Koran is not intended to be the voice of a violent religion, but as the saying goes with scripture, if you read it enough it'll tell you whatever you want it to. An extremely hostile minority shame the religion as a whole, it is not one that is violent by nature.