We must keep in mind that Tarot cards were originally made for trick taking card games long before they were used in esoteric or occult practices. If there's any real religion in the original Tarot, it was in the use of themes of the popular Catholicism of 15th century Italy to illustrate the trump suit. The actual underlying Tarot card game of which there has been numerous regional variants across continental Europe is suitable for anyone regardless of creed.
I also wish to mention the fact that all these Rider Waite Smith knock-offs we see in our popular media are not the only kinds of Tarot deck. In the 18th century, German card makers began making a type of Tarot using the same French suit signs as our Poker deck. The trump illustrations varied considerably from the earlier Latin suited design. French suited Tarot cards may depict animal or genre scenes and they are currently most often used in countries such as Austria and France. It would be good if more Americans were familiar with these cards. It would be especially good if more American Tarot writers were familiar with French suited Tarot cards as these writers seem to be only aware of American made cards and this parochial outlook cripples their ability to write on the topic from a more global perspective.
As an atheist game player myself with several blogs, forums, and groups concerning the Tarot family of card games, I have found that the rather small number of Tarot players in countries such as the United States and Great Britain, are often atheists or agnostics. This is due no doubt to the culturally biased context in which the Tarot is presented to most people living in the English speaking world.
Fundamentalist Christians tend to view the 78 card deck with much apprehension and are arguably more superstitious than the gullible folks who actually believe in the future predictions and too many of the fluffy Pagans and Tarot readers believe the common false histories of the Tarot and consider game playing to be a sacrilege to their cardboard Kabbalah and a threat to the virtual monopoly that some in the Tarot reading community wish to maintain over these cards. One of my main beefs against how the Tarot is presented is how too many of those promoting the use of Tarot cards for divination deny the existence of any other Tarot culture besides the divinatory Tarot. It is this promotion of cultural ignorance to which I most object.
It might sound arrogant to some but atheists, agnostics and other free thinkers are not as hindered by these Christian or Pagan prejudices and would therefore be free to enjoy the Tarot as the type of card game it was intended to be. I'm not claiming that non-believers are more knowledgeable than others about these cards but that they are free from the fundamentalist and fluffy ideologies which tend to oppose the use of Tarot for its original intended game playing purpose. While the Christians and Pagans play their ideological football game with the Tarot, my non-believing self will sit on the sidelines and enjoy the Tarot as a quite enjoyable trick taking game.