Here I'm continuing this discussion.
But what if Plantinga was a Muslim and he defended Islam with the same epistemological grounding?
Muslims and Christians don't have the same epistemological grounding. There's a reason why Plantinga's philosophy is described as "Reformed Epistemology." Also, Craig mentioned the inner testimony of the Holy Spirit. Last I read, Muslims don't believe in the Holy Spirit. Plantinga's and Craig's philosophy here is distinctly Christian.
This discussion seems centered around the idea of "personal" religious experience. People can believe that they had-or can claim to have had-some sort of "personal" experience with a supernatural being and can then say that because of that "personal" experience, they "know" that the supernatural being exists. Of course it goes without saying that when a person says that he or she had a "personal" experience with a supernatual being, this is never going to be enough, by itself, to convince any reasonable person that such a supernatural being actually exists. If a Muslim apologist says that he had a "personal" experience with Allah, this is not going to convince Bill Craig that Allah exists. Craig would certainly deny that this Muslim apologist had a "personal" experience with Allah. Craig would likely call it a delusion or would attribute it to demonic powers from his own Christian theology. So who cares about "personal" religious experience-apart from the person who has it? If "personal" religious experiences were to actually be considered reliable evidence for supernatural beings, then there is likely to be a multitude of supernatural beings out there since people claim all the time to have spoken to or to have otherwise had "personal" experiences with all sorts of supernatural beings. Does Frank Walton deny that these "personal" religious experiences are genuine? Does he believe that only Christian "personal" religious experiences are real?
I think it would be interesting to learn what, specifically, Bill Craig is referring to when he talks about personally experiencing God. Does he hear voices in his head, or does he see a bright light, or does he feel all warm and fuzzy inside? Does Craig described this "Inner Witness of the Holy Spirit" anywhere?
I haven't researched this to know. But I don't think a coherent understanding of this purported inner witness can be adequately described, since Christians who claim to have experienced this should've gained some knowledge as a result of it (i.e., some propositional beliefs about the divine being they experienced, and also, knowledge of what they as Christians should believe that confirms what they believe). Christians who claim to have had this experience must subsequently be able to explain why there are so many differing doctrinal beliefs among those Christians who claim to have had this same experience. These Christians must also distinguish their purportedly unique experience from the experience of people in all other non-Christian religions, or no religion at all. Either there is no content to this experience, in which case I seriously doubt it is a personal experience of some Divine Being at all (since we always know something about the person we have just met and what he wants us to do or believe), or, this witness is so muddled and weak as a religious experience that atheists can even deny they have even had one at all.