Since when is this a problem? For gods sake, let people fuck up and harm themselves if they're stupid enough to take the risks, or not.
I think it's fine to say "Remember, this is risky because of A, B and C, but here's how to do it anyways..." but straight up "If you have to ask, you shouldn't" seems so backwards and almost mean, especially when we talk about money which is mostly "easy come, easy go". Let the fool be parted with their money if that's what they want :)