Suppose I destroy the timeline, and create an identical one. Have I committed a moral evil? No, because nothing has been lost.

Suppose I destroy the timeline, and restart from an earlier point. Have I committed a moral evil? Very much yes. What was lost? To give only one person's example from Flight of the Navigator out of a planet of billions, out of a whole universe, the younger brother who was left behind had spent years - of personal growth, of creating value and memories - helping his parents with their quixotic search. And then bonding with the new younger "older" brother, rejoicing with his parents, marvelling at the space ship. And then he was erased.