I agree with your statement in regards to conspiracy theories and science, but there is a way to prove one way or the other when it comes to science. To choose to not believe that is a choice to reject evidence so we can in that case say they are absolutely incorrect.

This issue with morality is more difficult because what we're trying to "prove" is often something that is outside of the natural world. Say for example a forced uniform, or code of clothing like a Hijab. It's immoral to not wear one or to not cover your hair for religious reasons, but we (especially as atheists) see forcing people to wear something as immoral. To force someone to do anything is not right in our minds, but to others it's more important to respect God and to protect yourself from the wrath of God or from another immoral human who would want to sexually assault you (or the wrath of nosey neighbors that want to stone you for God.) It's very difficult to prove anything in that situation especially since it involves "Gods."

I don't really know how one could prove something is wrong when it comes to morality. I could imagine taking steps and at each step you ask "does this hurt someone?" but even then, going back to the Holocaust example, hurting someone to protect yourself could still be seen as the correct moral choice based on the framework your society is working within (again for anyone else reading, I'm not trying to defend Nazis lol). There are a base set of "facts" about the world that you would base your morality off of and the society you live within defines those "facts."

"The trolly problem" comes to mind as well. Hurting people is wrong no matter what, but we also believe hurting one person is morally correct when the other choice is hurting more people. Morality is so difficult to rationalize in all the various instances in which it arises lol I don't really mean to be arguing, it's just such a difficult topic to say one way or the other is "correct."