Contra Daniel, I don’t think it’s necessarily true that “there’s plenty more science fiction out there about utopian societies than there are about ones where a virtual lion eats the real people like in The Veldt.” Virtually every single sci-fi film that gets released these days (that is, the ones that aren’t about space smurfs who are, like, really in touch with nature) is about SCIENCE GONE WRONG and THAT WHICH MAN WAS NOT MEANT TO KNOW, etc. The vision of a utopian society isn’t the most overused science fiction plot in history: the plot of the very first science fiction novel, Frankenstein, is.
Except, of course, Frankenstein had a deeper point to make than technology bad. You can’t understand Frankenstein the novel without understanding the context in which it was written, post-enlightenment and twenty years after the French Revolution. The monster himself is the product of a whole new tradition in human thought: stronger, leaner, and smarter, but difficult to control and prone to develop on his own.
Point is, this concepts only last when they tap into something a little richer than just fear. Bad, didactic science fiction (re: the space smurfs) presents you with the answer to whatever question the movie’s asking before the plot even really begins. But good fiction–not just science fiction, but any fiction at all–asks the sort of questions that are far too difficult to answer on anything beyond the individual level, if that. That’s Bradbury’s legacy.