As for the big revelation that humanity had a hand in the Borg's birth, yeah that's something that needs to be locked down big time. Otherwise there's going to be a lot of pissed off races going for humans.
There's a difference between what Picard, Riker, and Dax know
, and what the three of them can prove
There's no way for them -- or anyone, for that matter -- to prove Hernandez's statements about the relationship between the Borg and the Caeliar. To an outside observer, what happened at the end is very simple -- Hernandez and the Caeliar made the Borg go all glowy before they went away.
In short, I'm sure the debate about the nature and origins of the Borg will continue within the Federation and throughout the galaxy post-Destiny