Hypothetically, science proves free will isn't real

[Edwardo Piet]

There's no way hard determinism could ever undermine rationality because whether hard determinism is true or not, what we have always deemed to be the concept of rationality is the same either way.

You can't be serious. If you don't have any choice about what you think then your thoughts could be anything at all for no reason in particular.

You don't understand determinism.

"No free choice" is not "no choice". Determinism is not fatalism. Our choices still exist and our will still exists whether our choices or will is free or not. Determinism means there is exactly one physically possible future at any given moment and there is but one causal chain with no possible alternatives. In other words: it means we cannot "do otherwsie". Fatalism is the denial of any choice at all by suggesting that determinism implies that we might as well give up and our choices don't matter "why get out of bed in the morning?" etc. It makes no sense because even if our decisions are determined, they still exist. It just means our decisions are part of the causal chain and not free, it does not mean they don't exist and do not matter. If I had not decided to write this post it would not have written itself, that does not mean that I decided to do it freely. I could be fully predetermined to decide to write this post but I still decided to write it.

I cannot possibly be serious? I am serious. And you can indeed possibly be serious too. In fact I have no doubt that you are. However, not only are you serious, you also seriously fail to grasp determinism and you're conflating it with fatalism.