#####The degree of certainty to which it is put forward is based on the fact that it has acheived the level of theory.#####
Or has it become ideologically entrenched? A psychology professor who calls homosexuality abnormal likely won't get tenure. Ditto for a biology professor who questions evolution. Scientists are no less subject to the zeitgeist than anyone else.
#####Could you state a "competing" theory?#####
Intelligent design, for one. But since science is defined in such a way as to exclude it, that one has no chance to pass through the filter. Feel free to offer evolution as a theory, but don't expect people to necessarily swallow it.