Partially biased because of the show Sense8, I believe that being a part of a Gaia-like entity doesn't necessarily mean losing what makes us essentially human. "What makes us human?" is a question in itself. Gaia has respect towards beliefs of individuals, which is why it surrendered its fate to Trevize. Making a leap of faith is quite a human thing to do, imo. Also, Gaia has expressed approval of Seldon's plan, which implies that the Second Empire will be established, only this time, with potential for its eternal longevity.Regarding the last statement of Trevize and also his decision on choosing Galaxia. I think it refered to the fact, that even if the alien threat was not yet present, the humanity as a whole is in danger of loosing it's humanity(or the part that made it human), and the solarians (represented trough the solarian child) were the example of that fact. So maybe Trevize made his decision in fear of the alienation inside humanity itself.