Contrary to popular belief, it has not been proven that Jesus existed
While this is technically true, I guess, it's highly misleading- while it hasn't been "
proven", as in, demonstrated beyond any reasonable doubt, it has been established as highly probable (more probable than the alternative, that Jesus did not exist), and largely by secular scholarship. There is a fair amount of evidence, primarily historical reports from pagan/Greek/Jewish/Roman sources from the first few centuries, that there was in fact a person at least
roughly corresponding to the person of Jesus Christ, as described by the Gospels, and not only that, but these writers appear to treat the subject as if it were a well-known fact in their time.
(now, importantly, this is NOT to say that there is any evidence this person rose from the dead, performed miracles, or was in any sense God or the Son of God- only that there was a Jew living in 1st century Judea who caused quite a ruckus with the religious and Roman authorities and likely went by the name Yeshua)
Right, although here again, the word "proof" is tricky; there have been many attempted "proofs" of the existence of God, and many of us are familiar with them from these very forums- but none of them can be said to be sound, and thus God's existence has not been "proven".
Alternatively, we can provide various proofs (and by "proof" I mean an argument)- which are at least
prima facie logically sound- that something like the Christian God cannot exist, even in principle.