[Houshalter]

That's true for everything, with the whole butterfly effect. Just opening the door to the time machine and walking outside is enough to change history completely. Imagine someone has sex in a different position or at a slightly different time. A different sperm reaches the egg, a different person is born. Not only will that affect all their descendants (which is pretty much the entire human race after a few centuries), but all the people they would have known or interacted with.

[afterburner]

It's the opposite of the butterfly effect, he's more likely arguing that WW2 was built on the frustrations and ideologies thrust forth as a result of WW1, so merely killing one angry officer isn't necessarily going to avoid one or another catastrophe involving war and genocide. WW2 might in fact have been unavoidable (not sure whether this is true or not, but it might be). Some other racist charismatic dude might just take his place, ready to harness whatever ill will there was around him/her. (Well, probably "him".)

[brokenparser]

Not sure if my attempted humour is that bad, or so advanced it wooshed straight over your heads.

[afterburner]

Changing the past while at the same time vanishing yourself from existence is still changing the past... but I will consider your proposed remedy when it comes up.