It is a common science fiction device that time travelers often set out on their adventures with a single goal in mind: to kill Hitler and prevent the Holocaust. It has become its own theme in the science fiction realm, and generally does not work out to the benefit of the characters.
Of interesting note is the fact that Hitler shows up in all of these time travel stories, yet there have been numerous other dictators who have taken profound tolls on the world. Stalin and Saddam Hussein spring immediately to mind, yet no one seems so set on going back in time to kill them.
Still, the annihilation of Hitler does not seem at first like a bad idea, and yet it quite possibly is one of the worst. Not just due to science fiction tropes regarding the nature of changing history during time travel, either. There are several reasons that his death would affect the world as we know it today.
First, there is the basic moral dilemma in taking a life. The characters in these sci-fi stories are generally regarded as heroes, not murderers. Even if one could bring themselves to take the life of a human being, when and where would it be appropriate to make the kill? Hitler did not physically force his soldiers to commit the Holocaust, so killing him after his rise to power might be moot. And certainly, even knowing his future, no heroic time traveler could be all too comfortable with the murder of anyone in their youth, The Guardian reports.
Also, Hitler could not have risen to power so easily if not for the depression that Germany entered in the aftermath of WWI. So if one were to pull off the assassination, who can say that someone else might not just take his place? What if his successor is even more powerful than he is? How many people would we have to kill in our time travels to get the desired result?
One sad and hard-to-face truth is that Nazi Germany gave us some incredible scientific innovations, some of which led to our better understanding of space-time (a fairly important concept if you like to travel across time and space killing tyrants). Not only that, but in a strange way Hitler brought a better sense of unification to the world. The Jews faced racism to large degrees even before the mass murder they faced in Germany, and WWII taught people to look at themselves to ensure they were not harboring any of the same character defects as the enemy. Not to say that the Holocaust itself was a good thing, but it is at the very least possible that its aftermath had some decent effects on human beings.
Either way, one thing those engaging in rogue time travel should try to remember is that the Allies did not lose the war. Hitler lost the war through fumbling strategies, ultimately opting to kill himself. The likely alternative to what the world would be without Hitler outside of the above possibilities is remarkably similar to the world we live in now—without Hitler. The odds are that his assassination in the past would either have unexpectedly grave results, or it just plain wouldn’t change a thing. That seems like something for the modern-day proponents of time travel to consider before hopping into the TARDIS and going off on a bloody rampage.