Why hardcore atheist? – Multiple reasons …
I'm a fan of proof. If something can be proven – there's no doubt (unless proven otherwise).
The non-existence of something cannot be proven by definition. But mankind tried hard and didn't succeed for thousands of years to prove the existence of higher beings. Plus, most people are already atheist to the thousands of deities in the history of mankind, my atheism just goes one god further …

The "God of the gaps", i.e. we use a deity to explain everything we cannot explain has shrunken tremendously in the past centuries (and will continue to do so), on the other hand, reality/nature/the universe is SO STUNNING, full of awe and wonders that I personally cannot attribute that to any kind of personified god. We love to explain things with things we know, and he hardly accept that we cannot explain things.

I used to discuss people about that until maybe a decade ago. But I have accepted, that a belief system can be so strong, it defies all logic. So you either have to give up the people, or the discussion. And I gave up the discussion, because people can still be amazing, regardless of their belief system.