One thing that always bothered me about The Federation was how they treated certain worlds and members.
Recall the TNG episode Journey's End where the Enterprise is sent to remove what amounted to some 'Space Native Americans' from a planet the Federation had given to Cardassians in a treaty. The inhabitants in question were members of the Federation (with all the rights that was supposed to confer) but they were (going to be) forced off the planet. The only way they could stay on their planet was to give in to the treaty and make themselves inhabitants of what was then a Cardassian planet (and arguably Cardassian property).
Then there is the TNG movie Insurrection. Where a group of settlers who are not Federation citizens were going to be transported off of their planet against their will. But Picard decides that they deserve to stay on the planet so the Enterprise destroys the Federation/alien ships that were sent to do the relocation (among other things and aliens).
So why is it the Federation wont fight for actual Federation members, but they will fight for some random civilization because of 'reasons'?
Ok I'm done with my Star Trek rant and feel like a terrible nerd now. Thank you for letting me vent and for the link. Nerd gland expressed.
Edit: For a laugh Google the Red Letter Media Harry Plinket review of Insurrection which goes deeper into this.
To be fair, the planet in Journey's End wasn't a full member but a colony world, which means they don't have the same rights as a full member. Plus, I think they just settled on that planet which would mean the planet isn't under Federation jurisdiction, just the citizenry (provided they're Fed citizens).
Additionally, the Cardies have either a similar or better military compared to the Federation, and the treaty helped prevent full out war (that later showed up, but in the form of the Dominion War). Giving up a few planets with small populations doesn't seem all that bad for stopping what could've been the largest war in the quadrant.
As for Insurrection, it's commonly accepted that Dougherty was working alone, without the support of the rest of Starfleet or the Federation. It's not implausible, considering he was an admiral and could very easily order ships places without much questioning.
The Son'a are nowhere near as advanced as the Cardassians, the Federation could easily take them if they tried to start something.
It was never firmly established that the Cardassians alone were a match for the Federation (much less so if the Klingons were involved). If they were, Captain Jellico's aggressive negotiations in "Chain of Command" wouldn't have worked. It's more a question of the Federation bending over backwards to avoid conflict.
In Insurrection, it's established that the rejuvenating radiation from the planet made the crew feel more youthful and fighty.
To be fair, some of the writers did a great job of creating brilliant episodes, despite the setting. My favorites are the DS9 episodes focused on Garak, many of which remind me of Phillip K Dick short stories, in that they make the viewer question the true motives (and natures) of all the characters, combined with inconclusive facts.
Oh yes! More than a few episodes from all eras are quite fun to watch.
But the universe, as a whole, disappoints.
I don't know if Paramount would have let them, but if the writer's for TNG (and DS9, and so on) had been free to ignore the canon from the preceding shows the entire thing would be much better.
"Same idea", they could have said "But we're not going to be constrained by what came before. Accept it on it's own terms."
tl;dr the Federation is a not a political union, its a human-dominated protection racket. Non-human worlds pay Earth for protection and Earth maintains a post-scarcity economy from living off the proceeds of tribute. In this context, the Prime Directive ensures ambitious captains don't takeover planets that are likely to be a net drain on resources.
That was entirely worth the time to read. Very interesting take on it and it also shows how damaged I am by online forums thinking it read like a perfect troll.
http://www.volokh.com/posts/1190182117.shtml