How many people would need to have seen Bigfoot for you to believe that he exists? There have been about 3500 alleged Bigfoot sightings since 1960.
If Christianity is true, the Holy Spirit exists. [John 15:26-27] Two billion people claim to be Christians. That means that two billion people believe that the Holy Spirit exists. And presumably, a percentage have had some sort of personal experience with him.
If two billion people had witnessed Bigfoot, would you believe he exists?
Bandwagon Fallacy: The obvious objection to this argument is that just because many people believe something, doesn’t make it true. But if you have many witnesses of something, I think it becomes more than that.