[DominikR]

There is no doubt in my mind that the EU negotiated this in secret because they knew that society would be opposed. They likely would have tried to ratify this treaty afterwards in a stealthy way by suppressing media coverage or "encouraging" media give it a positive spin.

But I cannot prove this, that's why I'm also listing a few reasons for secret negotiations that could be acceptable for those who are inclined to give the EU the benefit of the doubt.