I don't think sci-fi and fantasy are that clear-cut. A lot of fantasy is quite hopeful (the bad guys pretty much always lose at the end of the story), and it's kind of 50:50 whether it depicts the past as better or worse than it was. e.g. the shire in Lord of the Rings is practically a utopia, despite not being completely unrealistic for a pre-industrial society (it probably looks a lot more utopian than it is because most of the hobbit characters we know are aristocrats).

Literature is, generally, definitely not about happy feelings, though.