In regards to having or lacking spiritual convictions or faith, I usually look to the star. The star card to me has been the card about hope, spirituality and connection to a higher source in a wholly spiritual sense. The star reversed would be more of a lack of spirituality. The card reversed has indicated for people in the past that they have lost hope and lack a sense spirituality. They have lost touch with their spiritual/religious convictions which may have been a large part of their motivation and inspiration.
The heirophant on the other hand has been a card of structure, religion, a sense of belonging to the group; group reinforcement.
Then you have to think of the motives for this group mindset. The upright position of the heirophant being the need for or the act of participation in faith, belonging, and group conviction; a desire for stability, security, and family. In the reversed sense, to me, it is group identification for all the wrong reasons. You become swept up in a faith or group because that's what you are "supposed" to do. Fear of moving too far from conventional and acceptable practices, opinions and ideas due to a fear of being singled out and ostracized.
So, yes, I guess I can see how the card can represent an atheistic mindset or eclectic values that diverge from majority tradition, but the stone heavy and sometimes stubbornly traditional values that the heirophant exudes aren't completely able to be swept away. The reversed may be the atheist or the teenage pagan who keeps their new found faith or lack of faith on the down low, as to not upset their family or community. Those who pay only lip service to their supposed faith.