But couldn’t the religious experiences just be mental projections?
It is true that our experience is highly shaped by our conceptual framework and products of a process of interpretation. The trouble with this objection is that it is no different for non-religious experiences. If I see a tree, my conceptual framework shapes that perception, but that doesn’t make it dubious in any way.
In fact it would make it questionable if the experience wasn’t shaped by my conceptual framework, because that would probably mean that my cognitive processes weren’t working properly. Instead of making religious experience improbable, faith may be considered as giving a person access to religious experience.
One may also object that believers have religious experiences because they have a very strong desire for them. But many believers who have very strong desires for consoling experiences in prayer do not have them, and some have religious experiences although they do not believe. In fact the argument could be turned around. Perhaps unbelievers do not have any religious experiences because they have an inner resistance to belief in God.