[gwern]

> The OP was not talking about the magnitude of the differences, but the nature of them.

And what, pray tell, are the 'nature' of disorders like Cotard's syndrome?

> OP: "Look at that person who was born with no arms due to a birth defect. They're able to live a fairly normal, happy life. Maybe arms aren't essential to human happiness."

Try going back and reading what was said. Your paraphrase is incorrect. Here's a correct paraphrase:

"OP: look at that person born with no legs. They're able to lead a somewhat normal life. This shows that anyone claiming that there might be differences between the fingered and the fingerless such as in fine motor control is a moron - because a leg is so much larger than a finger!"

> I'll leave what this makes you a demonstration of as an exercise for the reader.

Well, it demonstrates you can't paraphrase or follow the logical structure of an argument. I'm not sure what I'm demonstrating; hopefully something good.