Good question. Simple answer it's irrational, however, sometimes irrational thoughts can give us emotional comfort. Faith in humanity, or faith that things will get better can be seen as good because it's an optimistic approach to life which leads to feelings of satisfaction, etc... however, it takes away a percentage of one's responsibility towards making life/humanity better, for example. However, whether something is good/bad may be relative but I rather not get into that. Imo, faith can give special privileges to dangerous thinking if promoted which can be detrimental to society creating diversion and indifference, even sociopathic behaviour. It can cause the gullible to believe in God(s) or even fairies. It is often misconstrued, mistaken for concepts such as hope and confidence. Faith that one will get better, however, can be beneficial as subliminal conditioning may trigger the release of hormones and affect people's immune responses, helping them to feel better.

To properly address this question, we must first define what faith is, with percise words that arent ambiguous or vague. Some use it interchangeably with belief, while others say it's belief based on no proof.