To me it looks like you use the same words but mean different things.
Unless you agree on the definition of: "sure/certainty" you cant discuss it.. At least not in any meaningful way.
Also, some people can have 0%/100% confidence in something. Others cant because they always take the possibility that they are wrong into the equation(no matter how small).
So to state that is it wrong to asses 100% certainty is incorrect, if it is a measure of perceived certainly and not probability. (why it is so important to define what the words mean in the context)
But it is also incorrect to say that you can have 100% confidence in something, since some people cant.
It is two fundamentally different perspectives.
This is my take on it anyhow.