Gridalthea ignorance cannot hurt anyone,but oblivion can,you just stated what you thought, and its from at least my point of view,the right thing,tarot came from others sources but we do use it cause the Wicca(Old Religion)is about learning and developing what already exist,predicting future is something that exist in humanity since they knew how to walk.
By the way what is supposed to teach in what they cal a coven is how to prepare herbs,philosofy,biology,psicology and various others things that in that age was considered magic!Imagine in that age someone could read every body movement of someone and knew when they were lieing?Isnt something only "Witches" could do?Indeed even today is considered by most people something really impossible to do such feat,though its proved wrong.
And tarot,you know,the first thing you learn in wiccan is no one can predict the future,but have a better understanding and acessment of the situation,the tarot help us by guiding our vision n unexpected ways,by random a figure can mean something to you while if another person reads the meaning just mutates,you dont see the future but you see the most probably ways you would go....its all about your personality.
Destiny or Fate doesnt exist in the way everyone believes,there isnt anything written about what will happen to you,but the path you may take is already written by your personality,it may change if your personality changes....its your decision that makes your future.