Is mankind worth saving? It’s one of the many profound things you’ll have time to ponder during “Voyagers” (2021), a slow-paced, space-based reenactment of “Lord of the Flies.” With their home succumbing to climate change, earthlings plan an 86-year mission to the nearest inhabitable planet. The eerily quiet spaceship is populated with test-tube babies turned twentysomethings who’ll need to produce two successive generations and won’t live to see touchdown. Colin Farrell plays their astronaut guidance counselor until the kids (finally) start getting a little fidgety and arise from their chemically assisted calm. Hormonal hijinks ensue, hitting all the predictable notes.