You are taking the words out of the context. When one says 'I believe that the value of the BTC will go up', it is usually backed up by comments about the previous drop of the price or one quotes a text he/she read somewhere or some smart guy that said so or something. So, comparing sentences 'I believe in God' and 'I believe in BTC' is ridiculous. Believing in BTC is usually justified by a statement, a fact that was read somewhere or someone's opinion. And every single investor or potential investor forms opinion based on the capacity and information. It doesn't come as a surprise to me that there are people investing in BTC like playing rullet, they think of it as a gamble so it is completely reasonable that they need to have faith in it