What does "the dangerous idea" refer to?

Possibly it acknowledges that there might be a creation without a Creator. It looks like a religious concept to me.

Can "without a Creator" be religious, Roger? It sounds landing on nowhere close to both theism and atheism.

PS. I don't get "what something is for" very well. Would anyone like to rewrite it for me?

No. Well, Darwin's 'dangerous idea' was evolution. A design without a designer is like a creation without a Creator. Possibly, I should have said anti-religious concept.

"what something is for" is the same as its purpose. Now, something having a purpose is getting close to the idea that it was created. If it was created with a purpose, that kind of implies a creator, doesn't it?

By the way, I've never read Darwin. I'm just applying common concepts.

i love the way roger is evolving

What is a hammer for? It's for hitting a nail. A hammer is for driving a nail into wood.
A screwdriver is used for driving a screwnail down.
A cushion is for making your seat more comfortable.