I honestly don't have an agenda. As I said, I believe that Jesus existed. But from a scholarly perspective (I work in the library at a Christian theological college) it's not enough to show that Tacitus had access to contemporary documents. To be scholarly rigourous you'd need to demonstrate that the information about Jesus came from those contemporary documents. And you can't. It's certainly possible that he got his information about Jesus from contemporary documents. But it's equally possible (and far more likely) that he's using information from later sources (such as Christian writings) to fill in the gaps. The likelihood of Jesus being mentioned by name in contemporary documents is small, given that he was fairly insignificant in his own lifetime (by contemporary standards). He was an intinerant Jewish rabbi with a small following, who was killed early in his ministry. It was only as his followers began spreading the word that people's understanding of Jesus' importance grew. There are certainly things that can be extrapolated from Tacitus' writings about Jesus. It provides a 2nd century source confirming what Christians at the time believed, and it confirms that Christians were well established in Rome at the time of Nero and distinguishable enough to be successfully blamed for the Great Fire. The fact that a noticable percentage of the population believed in Jesus around 30 years after his death can be taken as supporting the likelihood of his existance. To create a religion around a totally fictional character would likely take a longer gap between his supposed existance and the establishment of the religion.
My point is, that in the absence of any actual contemporary documents, there is no actual contemporary evidence for the existance of Jesus. Tacitus' writings (even if they are based on contemporary documents) can only count as second hand evidence, especially since they provide no information about Jesus that wasn't available from other Christian writings. That's not to say that Jesus didn't exist - as I said I certainly believe he did. And there are plenty of other historical figures for whom we have no contemporary evidence of their existance - a good example is Socrates. All of the information we have about him comes from people writing about him after he was dead. But we don't doubt his existence. Jesus seems to be the exception, probably because believing in his existence is linked to believing in his teachings, which then require a commitment.