The reason why it was negotiated in secret is because there never would have been a consensus. It's literally a learned best practice of trade diplomacy.
Land of the Free ...
How about instead saying: we believe in open democracy and so despite it slightly weakening our position we'll require negotiations to be open and require those ratifying the treaty to first have a free vote in their parliamentary houses [wherein one option will be to ratify following a referendum].
Now that would be spreading democracy.
A cynic might think that this was the first best option to secure the world against change following the 1%-protests to ensure rich capitalists maintain their position of power because "oh we can't tax this damaging activity because it makes these people poorer and they made us sign a treaty".
If you asked the people what they want on every bill no country could function. Every tax would get rejected, and every spending bill approved.
Similarly for asking each congressperson about each individual clause in the TPP.
Cynically, one might argue that it is, in practice, a (plutocratic) republic and not a democracy, I suppose.
Keeping the negotiation process secret allows it to be analyzed as a package.
It wasn't secret to the entities benefiting from it, only to the entities being hurt by it.