yeah, the "who does the crappy jobs?" argument is kind of a tricky one for utopian socialism. You'd have to either have an extra privilege system(you get something cool for doing them) or you'd have a fair system of rotation worked out where everyone had a turn.
Right. It doesn't turn out very utopian in practice. What "cool thing" would motivate you to service a cleaning robot that's stuck inside a sewage tank? [Is there NO other way the citizens of Utopia can take a trip to Disney World? Because if there is, even the most ardent Disney afficionados will take the easier option, and if there isn't, it's a pretty crappy Utopia, where you are forbidden to just save up and buy the fun things you want like a free person.]
What happened in the Soviet Union under Stalin is that large numbers of city dwellers were taken away at gunpoint to pick crops and live in deplorable camps as slaves. "Fair rotation" might mean five years of unpaid hard labor for you, and no problem for made members of the Communist Party.
Like I said, Roddenberry was naive. Every country that attemted to create a no-incentive Utopia became (in varying degrees, depending on how harsh they were) a citadel of poverty, misery, and injustice. The Soviet Union, Cambodia, North Korea... it doesn't work.