Playing devil's advocate here, what are the independent sources you speak of regarding the spead of christianity by 60AD? Josephus? Who or what else?
Roman authorities thoughout the empire recorded dealing with Christians (e.g. Roman historian Tacitus documented Nero's persecution of Christians after the fire of 64AD)
Fair enough. Don't take this the wrong way, but I would avoid using the Bible as a self authenticating sort of reference if you're looking to debate non-believers. From their perspective (perhaps not just theirs), just because the Bible (...Book of Acts etc) says Jesus was baptized by John the Baptist, crucified by Pilate...died and was buried...3 days he rose from the dead etc...doesn't mean from that perspective it happened. Just that the Bible says it did.
You're better off using sources like the one you cited above, if you wish to be persuasive with this group...assuming the independent source isn't getting his information from the "disputed" historical source or what not.
That's all I have to say about that.
