I like the approach taken by several authors from Asimov in "The End of Eternity" to Star Trek or Loki on TV: Time travel is not allowed except for entities that live outside of time in a way that is not meaningfully perceived by anyone else; When unsanctioned travel happens, it is easy to detect and retroactively suppress by these entities. Of course this can all be refuted or at least declared a transient state at most by the mess Time Cop is; Or how things end up in any of the other stories.