You're right. Everyone agrees that there is not one thing on earth every single person can agree on. However, by doing so, they all agree on one thing, ergo proving the original statement incorrect. Some will begin to see the error of their ways and state that this is the one thing everyone can agree on, while others will hold their ground that the original statement was correct, proving it correct by disagreeing with those who believe it is wrong.
Did I spend too much time thinking about this, only for it to end up entirely useless because the original statement ends up being correct anyway? Yes I did and I'm not sorry