The following form of argument has some initial plausibility:
Ordinarily, action type A is no better than action type B.
So, if there is no deontological prohibition against A, there is no deontological prohibition against B.
But here’s an interesting fact. One can have pairs of action types A and B such that:
under ordinary circumstances, A is worse than B, but
there is a deontological prohibition against B but not against A.
For instance, let A be a train engineer’s choosing not to brake a slow moving train ahead of a section of track on which there are ten innocents tied up. Let B be the train engineer’s shooting one innocent dead (knowingly, without divine permission, etc.).
Under ordinary circumstances, A is worse than B. But if Alice reliably informs the train engineer that she will murder fifty people if the engineer brakes, the engineer is permitted (and probably obligated) to refrain from braking. Hence there is no deontological prohibition against A. But if Alice informs the train engineer that she will murder fifty people if the engineer refuses to shoot the innocent, the engineer must still still refuse. There is a deontological prohibition against B.
So, while there is some correlation between ordinary worseness and deontological prohibition, that correlation has exceptions.