I never really had a problem with it, it was still set nearly a century after TOS, think how we look at ourselves from a hundred years ago, hell even only 30 years ago, surely it's just a goal for humanity to strive for - the abolition of war and famine etc.
I even believe we may get there one day, provided we make it out of this century. But material improvement is one thing; having it eliminate all conflict to the degree of virtual Nirvana is another. It closes off story possibilities and makes the setting less interesting. (They eventually realized that on TNG and tried to reintroduce a few snakes back into Eden here and there, but it was too timid and too late and never stuck.)
It also actually made Our Heroes less sympathetic to me, to a certain extent, in that it always seemed kind of self-satisfied for them to be wandering around -- Picard was particularly bad for it, but they all did it -- lecturing less well-off or less-enlightened cultures about how great they
have it back in the home country.