If you include sociological sf in your definition (which, I agree, you absolutely should), then Star Trek seems to qualify. The utopian society of the Federation is one of the key background facts of the franchise (assumed in TOS, explored in more depth in TNG, then deconstructed to some degree in DS9).
You're right about the technobabble, of course. However, that's often just a mask for the actual exploration of sociological/psychological concepts. And there was technological/hard-scientific stuff too: TOS's "City on the Edge of Forever" was a classic time travel story. The Borg were an examination of transhumanism (a biased one, of course, but still). The Mirror Universe episodes are another example.
That's why I emphasized the "taking that as its starting point" bit.
The old joke about space opera is that they're Westerns in space, with space ships substituted for horses and laser guns substituted for ordinary guns. Now if a writer literally created a series by doing that - saying "hey, let's make a Western in space and make these substitutions" - they wouldn't be exploring the social consequences of space ships and laser guns, they'd just be adding fancy tropes on a story in order to make it seem more cool.
Now Star Trek is definite...
Another month has passed and here is a new rationality quotes thread. The usual rules are: