Perhaps an even better explanation comes from Tim Lee over at Vox, who goes into
the history of these agreements, noting that the "free trade" stuff has mostly already been taken care of, as there aren't that many meaningful tariffs/trade barriers left. Instead, trade agreements have become a sort of secret playground for big corporations to abuse the process and force favorable regulations to be put in place around the globe. He discusses the history and how organized labor, the copyright industries, the pharmaceutical industries and more now basically use trade agreements as a secretive, anti-democratic process to force through regulations they want.
As the opportunities for trade liberalization have dwindled, the nature of trade agreements has shifted. They're no longer just about removing barriers to trade. They've become a mechanism for setting global economic rules more generally.
This trend is alarming to Simon Lester, a free trader at the Cato Ins ute. "We've added in these new issues that I'm skeptical of," he says. "It's not clear what the benefits are, and they cause a lot of controversy."
And this system for setting global rules has some serious defects. We expect the laws that govern our economic lives will be made in a transparent, representative, and accountable fashion. The TPP negotiation process is none of these — it's secretive, it's dominated by powerful insiders, and it provides little opportunity for public input.
If you make the facile assumption that the TPP is actually about free trade, then you might be confused about all the hubbub about it. If you actually take the time to understand that much of what's in there has nothing to do with free trade and, in fact, may be the opposite of free trade, you realize why there's so much concern.