No its not. What they believe is up to them, and affects only them. If Person A realizes that his beliefs are his alone and does not force them on others or perform actions which people who do not subscribe to his beliefs would find unpleasant, its perfectly alright.
Every person is spiritual. Whether that spirituality manifests itself in the form of organized religion or something else, thats a minor point.
Humans beings are fundamentally irrational beings. How can you explain that every single culture in all of human history has gods, rituals - a religion. The quest for meaning is present in all individuals, you could even say that that is our prupose an sentient beings.