Its fairly obvious the main Federation planets are very comfortable considering that you need to meet several criteria to be accepted into the Federation
Bajor was on the verge of being accepted into the Federation, and it really didn't sound like a very nice place. Ardana seem nice only for a portion of the population. Vulcan had some harsh social practices too.
A planet could be brought into the Federation for many different reasons, like wanting to protect it (Bajor), or because it possessed a unique resource (Ardana), or hypothetically because it had a large war fleet during a time when the Federation needed more than they had. Or as a political move against someone like the Klingons.
But if your one government is like [insert bad Earth government here] then that's no promise of "nice."including having a single world government
