You still can't add.
If the GDP of the US is 11 Trillion, and the GDP of the FTAA is 10 Trillion, That means that the GDP of all the other nations of FTAA outside the US have a NEGATIVE GDP, WHICH DRAWS DOWN the total GDP. So, basically, we in the US, would be subsidizing those extra 500 million people from our GDP.
The zero-sum game. The last refuge of a protectionist.