Requiring a "social or philosophical significance" card to gain entry into a "best sci-fi series ever" discussion seems rather counterproductive. There are plenty of reasons why I don't think Firefly is the "best sci-fi show ever" but none of them have to do with its social or philosophical significance. If anything the enduring, almost rabid, popularity the show continues to enjoy shows that, clearly, the characters and stories are, somehow, resonating with viewers. That speaks to a fundamental social significance.
This.
It's probably a measure of the show's success that we're still debating it years later. I don't see a lot of threads about Threshold, Flashforward, or any number of other one-season wonders.
There also seems to be an odd conversational drift going on. Someone starts out complaining that he can't root for Mal and the gang unless they're fighting a truly evil Alliance. This somehow morphs into the argument that they needed a grand cause or goal to be worth watching. And now FF needs to have "philosophical significance" to be taken seriously?
It's a fun show that connected with a lot of fans.
Works for me.