(1) Religious experience is an individual personal experience
(2) Religious symbols are cultural
(3) scientific knowledge is far from proving a gene for religion
(4) therefore, we should not expect to find that mystical experience is universal
(5) we do find that mystical experiences are universal in the nature of what is experienced.
(6) Therefore, we are rationally warranted in thinking that there is an external stimulus being experienced.
(7)Since universal mystical experience leads people to faith, the content of it is about God, and is life transforming we are warranted in the assumption that this external stimulus experienced is God
the main body of the argument is developed in an essay here:
see "The M Scale And The Universal Nature of Mystical Experience."
An in Depth Article Summarizing my book (the Trace of God) and documenting the points Made in this argument.
see supporting material:
The Brain structure Objection
Science is far from proof that religion is genetic
Arguments and Essays Defending my Religious Experience Arguments.