Look, being de-assimilated is NOT the huge emasculation everyone thinks it is because we knew it was possible from the very first time we ever saw assimilation. Picard got de-assimilated between scenes, all he had were some bandages on his face! His real trauma was the mental one, and what the Borg forced him to do (slaughter thousands, nearly destroy Earth) none of which happened to Janeway and co (they weren't used to kill people or destroy Earth).
Nearly everything about Unimatrix was set up from prior episodes:
1) Renegade Borg? We saw how it happened in "I, Borg" and "Descent" except here it's beneficial rather than to create a new threat.
2) Being able to develop ways of resisting assimilation? They had Crushers' studies of Locutus and Hugh, as well as their own studies of Seven and other Borg tech. It's silly to think that they wouldn't even try to create some vaccination against assimilation.
Hell, maybe it's just because VOY played an important role in this story that riles people up. If it had been Hugh and his group of Rebel Borg who cooked up the scheme and VOY offered to help, the audience wouldn't have been so pissed.