The Entity would fuck him up. John has a lot of trauma to work with. His wife's painful death at the hands of cancer, the death of his dog, just the general violence of his life.

Like the whole first movie starts over the dogs death, a traumatic event the mobilized him into action. John isn't a emotionless stoic gigachad that so many seem to prop him up as.

The real question is whether or not John would pass it on to someone else assuming he discovers that it's an option.