Well... first of all, I need to know what kind of Federation we're talking about. Chances are, if it is a take it or leave it proposition, I'll decline. If it is a global economic and military order and I have to accept it, chances are I will. In any case, "a federation" could mean anything. It could be a gang full of roudy dudes that mug elderly people, for that matter, and if that were the case, I certainly would not join. If your question is whether I would cooperate with the UFP if it were a real organization as portrayed in Star Trek, then the answer is yes, I would. Of course, it isn't ever as simple as just "getting it started." There are always degrees of good or bad and changing patterns of force (admittedly coining an episode). As an example, the United States is kind of like the Federation in certain aspects, but falls short in others. What would it take? I suppose fundamental civil liberties and human rights are the best way to sum it up quickly.
I'd join. All I'd ask is a tall ship, and a star to steer her by. (I don't think I'd have a choice. I'm Terran. Not much of a Federation if it doesn't include Earth, is it? )
Ah yes however if it was to start it would not start out as a complete, set out organisation, surely it would have some of the ground ideas but it would organically evolve. To grow and evolve it would need people and ideas.
I would join if I were given command of the fleet's most state-of-the-art ship and sent into the unknown for multi-year missions where I'd meet up with hot chicks in body paint on the occasional diplomatic contact assignment and be able to save the day by delegating the hard stuff to my senior officers.
A federation of what? The Federation of Star Trek? With aliens? Without aliens? Is it a political question, a science-fiction one, or something else entirely?
You forget an essential ingredient - a technology advanced enough to make post-scarcity economy feasible.
If we're talking about political organizing in real life, without the science fiction-y parts of Star Trek -- aliens, warp drive, and the like -- the real question is, on what basis would you support your country joining a United Earth-type planetary state?
To start with, increased economic prosperity (heralding an increased standard of living) - which will come with access to advanced manufacturing technology, aid programs, etc. Of course, the problem is never so simple - in any societal transformation of such anvergure, a large part of the population will loose their now obsolete jobs, etc. Civil rights/liberties will also be a powerful motivator if we're talking about a dictatorial country (where you have the rather large problem of detroning the dictatorial ruling class - a feat whose cost will be blood, if it is at all possible).
When these basic treads come around every once a while, it seem to lock in on "post-scarcity economy" replicators, no money. But a dictatorship could provide all these things. " ... on what basis would you support your country joining a United Earth-type planetary state?" The new nation/state would have to be as free as the current society I find myself in, not just in terms of government, that's part of it yes, but the overall society. Reverse the question, what would you be willing to surrender to obtain a slit in the wall that dishes up free whatever? This Federation. Can I move around without being protected? Can I move around without getting permission? Can I get a job, house, food, clothes, health care without these things being provided by "the state"? The city I live in has a police force, but I can walk around at night without needing a escort through most of it. Saudi Arabian laws require women to have a male escort when walking outside, partly because it a paternalistic culture, but also because women will almost automatically be assaulted if alone. There are many nations and cultures I can see the United States joining with into a federation, but right now not with all of them.
Well say a federation loosely based on what we all know and love,however if it was today we wouldn't have things like replicators to make things easy but many of the concepts could easily be incorporated, what would you hope to see in such a society ?