Humanity had FTL in the Dune past, but it was connected to the machine intelligences that were destroyed in the Butlerian jihad -- or so I seem to remember. As with the mentats replacing computing & expert systems, navigators were a biological alternative to the AI navigators of the past.
"War is an ugly thing but not the ugliest of things; the decayed and degraded state of moral and patriotic feelings which thinks that nothing is worth war is much worse. A man who has nothing for which he is willing to fight, nothing which is more important than his own personal safety, is a miserable creature and has no chance of being free unless made and kept so by the exertions of better men than himself."
John Stuart Mill