Why you think I should have to prove a logical necessity is beyond me. But I'll humor you for a moment - as long as you're not expecting me to prove something 100%. Again, I can't even prove that you exist. Here again is the rule of conscience:
If I feel certain that action-A is evil, and B is good, I should opt for B.
Certainty is the opposite of doubt. Therefore a reasonably equivalent paraphrase would be this.
If I have doubts about whether action-A is good, but feel certain that action-B is good, it would be best to go with B.
I'm pretty sure that's what Paul stipulated at Romans 14:23:
"The one who has doubts is condemned if he eats, because his eating is not from faith; and everything that is not from faith is sin."
In that verse, Paul defines righteousness, not in terms of specific laws, but in terms of whether a man feels certain, on the one hand, or feels doubts on the other.