A common trend in the arguments of Jesus Mythicists is to point to any similarity between Jesus and a myth that preceded the first century A.D. and conclude that Christians borrowed from the myth. The line of reasoning goes something like this:
1. The narratives of Jesus have similarities to the myth of Osiris. (Premise)
2. Osiris preceded Jesus. (Premise)
3. Therefore, the narratives of Jesus were borrowed from the myth of Osiris. (From 1 and 2)
4. If the content of a narrative is borrowed from a myth, the narrative is also a myth and hence false. (Premise)
5. Therefore, the narratives of Jesus are mythical and false. (From 3 and 4)
Of course, no actual proponent of Jesus Mythicism would put the argument that way, and for good reason. For one, the argument is obviously invalid. (3) does not follow from (1) and (2). Moreover, (4) is demonstrably false. How many sober historians would conclude that Edward I of England is mythical simply because there are aspects of his life similar to that of the mythical King Arthur?
What the Jesus Mythicist position does, in effect, is prevent debate about the historicity of the life of Jesus from even getting off the ground. After all, why bother discussing the merits of the Gospels' empty tomb accounts when the very resurrection of Jesus itself can be dismissed as mythical from the start?