I am not sure I see how fairness fits into it. First, therapists know most people who come to see a therapist have some difficulty and they still chose to do the job of being a therapist. Secondly, the reason a therapist must prove they are trustworthy is because of how the game is set up. A client is supposed to go in, tell the therapist all sorts of horrible things about themselves, with no reciprocity like in a real relationship. The therapist absolutely must prove step by step that they are worthy of that information. It is not always blaming the therapist for past situations where trust was violated. Going in and trusting a total stranger without some assurance of safety or working up to levels of safe trusting is simply dangerous.