Many time travelers, especially novice travelers from cultures where time travel isn't frequent, hold themselves to the idea that the "past" is sacrosanct. The logic goes that if you change anything in the past, even something small, you may find your "present" radically altered. In the extreme, the argument goes, that people you know and love may no longer have been born, and that therefore making changes in the past is tantamount to murder.

This type of thinking is hopelessly mired in tempocentrism -- the belief that what you think of as the "present" is some how an objective reality that the time stream is supposed to react to. It is true that moving earlier into a timestream and making changes often results in domino effect changes downstream from that moment, into the travelers "present" and "future". But, honestly, this is no different than actions taken by non-time travelers. We all make choices which affect our time stream's future.

Take, for example, two people who meet and fall in love and have children. If you go back in time and cause them not to meet, you may be in some way "killing" their future children. But, that's also true if you aren't a time traveler, and you stop them from meeting. Anything we do has the potential of "changing the future", and for the time traveler it's no different.

It's understandable that a time traveler may not want to change his "present" time frame. But that's more of a self-centered, ethical, consideration than it is a broader moral absolute. Some rare time travelers come to terms with changing their time stream for the better, even it means they no longer get to see the ones they loved from their own timeline. This frees them to operate for the greater good. Far from being evil "murderers", these time travelers are self-sacrificing martyrs -- who give up any hope for personal happiness in order to make changes for the better in their own time lines.