I think it's fair to say that there are two seemingly incompatible aesthetics in the field, both products of the Enlightenment and each associated with one side or the other in its most specialised form -- the Rationalism associated with Hard SF and the Romanticism associated with High Fantasy. Both of these fictional forms have been segregated out from the field in general. They are, I would argue, valid "genres" in a way that SF and Fantasy are not. And the aesthetics they align themselves with are old enough and strong enough that I think the field of SF/F can't help but be affected by that centuries-old rift. Their argument carries on into our work and it's effect is powerful enough that we often have to make a choice -- or have the choice made for us -- as to which side we're on....
...The Rationalism of Wells is counter-pointed by the Romanticism of Verne. In the Gernsback-Campbell era when the term Science Fiction was born, those two aesthetics were already in deep collaboration. Romantic adventures fleshed with Rationalist science. Rationalist science extrapolated into Romantic adventures. Hell, from Frankenstein onwards this has been a field where the dynamic power of the fiction resides in the interaction of those aesthetics. Is Frankenstein Science Fiction? Fantasy? Horror? Or is it, like Bradbury's "The Veldt", all of the above?
For the record, I'm with Hal. Except he said it much better than I did.