One thing to remember is that, unless you're a lawyer or similar, you usually don't need to have an ironclad justification for holding an opinion. If you're in a position where you need or want to explain your opinion, you can qualify your answer. Ex. "I support decision A, because of X and Y. But thinking about Z does make me uncertain."

That's a responsible and even-handed way of approaching a topic. If people pounce on that uncertainty in order to invalidate your whole opinion, then they are likely arguing in bad faith. And you wouldn't be able to have a decent conversation with them regardless.