If humans are all moral and don't need a God to be the standard, you can't say that anything anyone has ever done is immoral or evil. This is a lot of words to basically say nothing.
Discussion
Immorality and evil is subjective, so yes, you are correct. All humans act in a way they believe is good, whether most agree or not is up to everyone else. Dictating what is right and wrong is exactly what gets us to a point of corruption down the line, because now you have a "moral high ground" to defend any action. If you reject having a higher king you give yourself agency to parse and decide for yourself what is right and wrong. That can be scary, but ultimately what an individual and human collective decides is right and wrong should be up to them.
History also shows that if something is seen as wrong, it will be attacked, and whatever leads to the best outcome for all will typically win out. Nazism, for example, was set to fail because it's ideological and philosophical foundation is more harmful than helpful for humanity as a whole and was acted out on a zero-sum basis. The values in religion are beautiful because they paint the incentives of cooperation in a digestible way, but they innately exist and don't require a "God" to be true. Humans created that higher class to justify their control over others at scale.
I also think God is a fine thing to believe in; it's most definitely better than the state, politics, materialism, what have you. Whatever encourages unity and cooperation is cool with me; religion just has traits and a history that show it's a corruptable solution.
Nazism didn't fail bc it caused more harm, it failed bc they were fighting a war on multiple fronts. History shows several empires that caused more harm but had power so they persisted.
Also how can you say Nazism was harmful if everything is subjective?
To be clear, I agree that fighting occurs when there are differences in where people draw the lines of truth and morality. But if you say there is none, then you can't ever say something is wrong, and then at that point, what are we even talking about? There's no utopia out there where people all just hold hands and love each other bc it's better for the species
Again, it's up to people to decide what is right and wrong and act on it; I'm merely pointing out that you don't have to look up to some higher entity to allow you to do so or dictate the dichotomy. If the whole world thought murdering people was right, they would act on that and it would be seen as normal, but it wouldn't win out as an ideology for humanity over time as it leaves the world with less people working together. The outcomes over the long-run realize what was "right" and "wrong."
And I also don't believe in utopia (at least not in this life) but humanity trends towards more and more cooperation despite the pain along the way. As physical beings, we don't have the foresight or understanding to allow our ego to dissolve and stop focusing highly on our individual existence, but very very slowly we're making our way there.
Yet those empires fell. Sure, you can pick apart all the details and say this or that as to why Nazism fell, bht I'm not arguing for the reason it fell; I'm saying it was doomed to fail from the start because it was not as effective at unify humanity in the long-run.
And me saying it's harmful is my opinion, and there were obviously people who thought otherwise. Both sides are part of it being subjective.