When you bring an example for "people stick to negative attitudes even when the things improve or are not like another bad thing", and the example you bring is actually a really bad thing – out of state tribunals are fully unacceptable, also in the way CETA modeled them – then it is very valid to question that example. It could be that your whole observation is wrong, that people do not really stick to negative perspectives, but rather that you became unwilling to see them as valid.
Your Python3 example works for me. But CETA does not. It just does not support your point.
If you consider where CETA started and where it ended, the transparent tribunal solved the initial complaints same as with the restrictions on when you can sue. That now the new tribunals are also not good enough is a moved goalpost.
You really think that's true for everyone, or are you just looking at a subset of complaints?
There have been huge protests against TTIP and CETA in Germany and around Europe, and you can't resolve their legitimate concerns by saying "excuse me sir, but by your own logic, you just proved my point".
Your Python3 example works for me. But CETA does not. It just does not support your point.