Under "Fast Track" Congress still has final authority to accept or reject any trade agreement the administration negotiates. The opponents of Fast Track are those politicians who, like the trade unions and other protectionists, do not want any agreement, anytime, with anybody. That is a valid political position to take, and I assume it is one you agree with. That's fine. Even Mr. Smoot and Mr. Hawley had rights to their opinions.
But speaking as someone whose livelihood depends on foreign trade, I want the president to be able to negotiate without Congress breathing down his neck, but fully accept that they must and should have the last word.
And we should have positively byzantine trade treaties, a legal labyrinth for businessmen because....???