When we talk about sensory experiences, we sometimes talk about how such experiences can give justification to a belief. For example, me seeing a cat with my eyes provides a reason/justification for me to believe that there is a cat in front of me. This same move is commonly made when it comes to religious belief/experiences.
But, some apologists like to go further and argue that religious experience can actually serve as an argument for God’s existence, which means that these experiences can convince others of the existence of God*.
One problem with this strategy is that there are conflicting religious experiences, which we wouldn’t predict on the hypothesis of theism.
The second problem is that, if God exists, we would expect more people to have religious experiences, but not everyone does have such religious experiences.
Thirdly, many of these religious experiences of God are ambiguous and vague, which is expected on the no-God hypothesis.
Fourthly, we would expect people to have some religious experiences, whether or not those experiences match up with reality. This is evident from the fact that not all religious experiences, and/or the interpretations of those experiences, can be true.
Finally, it is unclear why the God hypothesis would predict that we would see religious experiences in the form of what we see in the actual world. If anything, one might expect to be constantly experiencing God in a very strong form, but that’s not we observe.
*I am talking about classical theism.