I don't know how good of an argument this is, but I've always found it odd that Islam--around its very beginning--took so long to spread and could only be spread by violence. Most people thought Muhammed was a lunatic and he even doubted his revelations himself (till his wife told him otherwise) and he only had like a few legitimate followers who believed him. Everyone else was only converted through force--hence the invasion of Mecca. On the other hand, Jesus and His early Apostles converted large groups of people numbering in the 2,000-5,000's at a time, and that was through legitimate conversion, not force. This is a VERY good reason to object to some of Islam's sources. If people thought it was unreliable back then, maybe they were right.