"What a moronic statement. I stopped reading after this bit of tripe."
I didn't see anything moronic about it; this has been the theme of any number of science fiction books and films. I've never agreed with it myself, entertaining and dramatic though it might be. I've never thought that this dimension, or any other, could possibly be that fragile.
The point is that people wouldn't suddenly diappear in front of you if their grandparents were killed before their parents were born. They would simple not even exist in your memory to begin with, since they never would have existed. Any reliance on SciFi writting is laughable to the point of being ignored.