The importance of Free Will

Hi all - reading a thread recently about “proof of God”. One commenter suggested chemistry, and more broadly perfect natural design suggests there is a God which I found interesting.

But then I got to thinking about tragedy like childhood cancer (and how could that fit the perfect design theory).

If I’m understanding correctly, sin, tragedy, etc. is a consequence of original sin.

Original sin happened because God gave us free will. So if I’m understanding correctly, there was no other way for God to design us and truly grasp His love without free will - it was/is critically important and therefor free will is a crucial part of perfect design.

Generally I get that but still going back to the childhood cancer example, I don’t get why that should be a consequence of original sin and I don’t get how that is perfect design then.