It's only 'laid back and fun' at the start. It's presentation in the initial episodes is, indeed, sprightly slice-of-life. Although, upon rewatching, I'm recognising all the groundwork for the later political developments. For example, the episode where Fee Carmichael just wants to smoke but keeps getting prevented by terrorists who blow up the smoking rooms is chuckle-worthy. At the same time, it introduces the viewer to the political unrest simmering in the background of this unified world order.
Later, developments become far more sobering, more focused on Hachimaki's personal struggles, and the illuminating theme of how science/progress becomes a tool or victim of politics. As an example, I watched last night the episode about the El-Tanikan who just wants to get his suit approved by international standards to help his country's development. He is prevented by the fact that his home has now been invaded by the world government. As he's about to be arrested, he watches earth from space and says something like, 'I can't see any border lines from here'. Down below, the impoverished people who gave their all to get him to space, are facing tanks and bombs. (My full review:
http://www.anime-planet.com/reviews/a589.html)
I certainly would not recommend this show to everyone. If it doesn't sound like your thing, by all means try Moonlight Mile, which has absolutely nothing in common with it. But you're less likely to get bullied for watching Planetes than the supposedly stereotypical Moonlight Mile.