Convincing Theists to Abandon Theism?

This is intended as a conversation piece in response to a rather interesting blog post by philosophical theologian Stephen J. Graham.

Despite being quite very opposed to Stephens views, I really enjoy interacting with him on Twitter.  Most exchanges we have are very respectful and we seem agree on a variety of topics not related to theism.

His blog post really caught my eye since he tries to answer philosopher Anthony Flew's challenge of asking what it would take to abandon theism.

Stephen's answer is quite candid, pointing out he doesn't really know exactly what it is that grounds his theism but never the less he gives two things which could undermine his Christian beliefs:

1. Showing the concept of god is incoherent.
2. Conclusive historical evidence of Jesus not existing or the resurrection being a hoax.

Stephen also goes on to describe how a traumatic event in his life could make the problem of gratuitous evil more convincing to him personally, which would undermine his belief in god.  There isn't too much I would say in response to that point, so I'd like to focus on the first two.