...if they were NOT secret and people would know what's in those contracts, the support would certainly not rise.
The mere idea alone to circumvent the judicial system and instead establish an "arbitration system" that's basically controlled by the international corporations should already be enough to ensure opposition by pretty much anyone.
Bluntly, any government in favor of this is basically giving up the sovereignty of the country entrusted to them and should be treated as such with the relevant laws. As long as the judges are still in charge.