One thing I've seen people debate a lot in the past is whether Michael Eddington's speech from DS9 about the Federation being an insidious version of the Borg which assimilates cultures, but in a voluntary way, has any truth to it. The most interesting part of Eddington's argument is that the Federation is basically a galactic empire that conquers cultures with kindness, and in those cases where the kindness doesn't work (e.g., the Klingons, Romulans, Cardassians, etc.), they may outwardly respect those culture's choice to go their own way, but secretly they only see it as a matter of time until they "take their rightful place on the Federation Council."
As I've gotten older, I could see the situation from TNG's "First Contact" (the episode, not the movie) being more and more true. If some alien version of the Federation made contact with Earth tomorrow, I think it would go about as well as it did in that story, if not worse. There would be people who would love the opportunities it would offer to become "part of the chorus" and expand our way of looking at the galaxy.
BUT ... I also think the other aspects of the episode would ABSOLUTELY happen. There would be vigorous opposition to the idea of first contact, with people who would worry about the effects to human cultures, and reject the idea on principles of sovereignty, conflicts with philosophical, economic and religious belief, and phrases like "human purity" and "a human future for humans" being thrown around to support an isolationist stance.