Be careful that you aren't projecting a preconception here, because what you think you see does not exist: no one has expressed anything anywhere close to "unquestioned belief".Unquestioned belief in existence of BH displayed by many here is breath taking.
By their nature, black holes cut us off from observation of many of their features/structure, leaving the list of observable features relatively short. So we'll never have anywhere close to the certainty I have in, for example, the existence of my car. And even at that, no scientist would ever claim 100% proof of a theory.
One small caveat: a black hole is a theoretically predicted object and the term is just a name. Jupiter was Jupiter long before humans knew it wasn't a God's flaming chariott. For black holes, the name and prediction came before the detection, but it is possible that the name will remain even if the theory is found to be largely wrong. Why? Because the objects are real/exist (to close to the maximum level of scientific certainty) and even if their description changes, it is hard to unstick a name. Jupiter is still Jupiter even though we now know it isn't a God.