I got into a discussion with a couple other forum members a few weeks ago over the whether the Jesus of Nazareth actually existed or not. Both sides brought up points, me citing references from Suetonius, Tacitus, and Pliny the Younger while others brought up the lack of contemporary sources and the Testimonium Flavianum, forged by Christians and allegedly attributed to Flavius Josephus.
My question is, outside of the lack of contemporary historical references, why is the historicity of Jesus called into question, what kind of evidence against the existence of Jesus can be provided, and where and how did this theory spring up?