Without secrecy concerning the details during negotiation, it would be very very hard to make trade agreements. Negotiation involves a lot of give and take. If that was all public, then as soon as our negotiators conceded on, say, some term that was going to help our automobile industry in order to gain some term that will help our garment industry, there would be a huge outcry from the automobile industry, and soon the negotiators would come under intense pressure to get that pro-automobile industry term back.
Secrecy, at least concerning the details, during negotiation gives the negotiators a better opportunity to work out a deal that best serves the interests of the country as a whole.
Note that I'm only talking about secrecy during negotiation. The result of the negotiations should be made public well before Congress votes on it, to give the country time to decide on whether to accept or not.
But as instantiated, the secrecy that the US Trade Reprentative uses and imposes is not this kind of secrecy at all. At least as near as those of us outside the TPP/ACTA negotiations can tell. The treaties do not become public until after they're negotiated and signed.
From leaked documents, it appears that inside the negotiations, there's really not the kind of secrecy you're imagining. Every part to ACTA, for example, just marked it up as they thought it should be, and then there was a lot of something (not public) to get to a final draft. That's not keeping a maximum (or minimum) position secret in order to gain advantage, that's just deciding how much of something can be foisted upon the global public without causing a revolution.
From my standpoint, the secrecy we get is of no use to anyone but corporate fat cats and insiders.
Secrecy, at least concerning the details, during negotiation gives the negotiators a better opportunity to work out a deal that best serves the interests of the country as a whole.
Note that I'm only talking about secrecy during negotiation. The result of the negotiations should be made public well before Congress votes on it, to give the country time to decide on whether to accept or not.