It means the same thing as "absolute agreement" because of the word "more". There is no way that my agreement could be increased.
Here's a tougher one for you. We have an expession "I couldn't care less". It is the opposite of your expression. There is no way that my level of caring could decrease. I don't care at all.
It has become common among certain groups to change that into "I could care less" with the identical meaning. Many say that those who use this form are expessing irony. In my view, most of the people who use it could not define "irony". Whatever the reason, we have two statements that are opposite in form but identical in meaning.
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