Even if a person could travel back in time, if he/she tries to prevent an event, it causes alterations in the "time-line" between that point and the current time from which he/she came from. This creates contradictory situations like this simple example:
Person C goes back in time to prevent event D. In the process, he prevents person A (dad) and person B (mom) from ever meeting and producing person C (time traveler). Therefore, person C never existed to prevent event D.
Perhaps if time was altered so that EVERYONE goes back in time, that would be more plausible. However, it is still science-fiction as "do-overs" do not exist in real life.
If by chance I am wrong, I doubt either of us will be alive to see it, but be sure to look me up and say I was wrong in any reversed timelines.