The problem is the magnitude of what is being negotiated - and the fast track, “take it or leave it” approach.
The tenor of the opposition arguments is that lobbyists with an “in” are helping write the treaty, yet the lawmakers who must approve it are kept in the dark until the full text is “sprung” on them, with of course urgent appeals to pass as soon as possible to limit debate and avoid finding loopholes.
For example -
Copyright - it’s believed the USA is pushing for extreme copyright language which would mean that copyright in one country is valid in another. So if Mickey Mouse or Sherlock Holmes or “Happy Birthday” lobbies hard enough for another 50 years of protection, even retroactive removal from the public domain, every signatory must recognize that.
The same fear applies to patents and trademarks. Presumably, what is now civil issues will become criminal issues to all signatories. Canada, for example, has lesser patent terms and rights to drugs and mandatory generic licensing after that. Under the TPP, they would have to respect other countries’ limits.
There’s the “corporate sovereignty” issue, where if a country’s laws impact a corporation’s profit or ability to do business, then the corporation can sue for redress - so if a country bans asbestos, or requires scare labelling for cigarettes, or has more strict health standards for a food product, the corporation has the option to sue and get repaid for their lost business opportunity.
Yes, the negotiations tend to be secret, but we seem to have known more about the Iran nuclear negotiations than we do about this deal. Why? It’s not like the negotiations are “top secret”. All the negotiation teams know what’s going on. Congressman A spilling the beans won’t wreck the USA’s negotiation advantage, the rest of the negotiators for the other countries know. It’s not like START, where how much and how powerful and how capable our arsenal is, is a key negotiation issue - it’s trade, all the numbers are published statistics. So the goal is to hide the content of the agreement from the public, completely. That says an awful lot about how “interesting” the content is.
The idea is to spring it on congress and hope it passes before people realize the ramifications of what they agreed to. (hence the big push for “fast track” where the treaty cannot be amended).