A Star Trek theme which recurs is the fantasy of time travel, and a subtheme is that of preserving the timeline (i.e. not doing anything while you're gallivanting through time that will change future events). I've thought about this a bit over the years, and find the concept of Timeline Preservation to be mostly absurd, as somewhat insignificant events can significantly change history.
An egregious example would be this theory: the 2002 bankruptcy of US Airlines is due to a pint of ale in 1836 Austria.(History students will grasp this faster than others:) due to a chance encounter (let's assume a carriage driver was hungover .. one too many pints of ale the night before), Maria Anna Schicklgruber met a man at the carriage stop, "hooked up" with him and eventually gave birth to Alois Schicklgruber.
Alois Schicklgruber and Klara Polzl (Alois' niece!) were the parents of Adolf Hitler, whose Holocaust so enraged the world that the state of Israel (a safe haven for Jews) was mandated in 1945. Further, US support of Israel inspired Arab militants (including a Saudi named Osama bin Laden) to attack the World Trade Center on 9/11/2001, creating such havoc in the airline industry that several carriers were thrown into economic chaos, including US Airways.
If, in 1836, the bartender had sent the carriage driver home without that last pint, and he'd been on time the next morning, would that have kept Delta Airlines out of bankruptcy, and saved the lives of 60 million people (total deaths in World War II). Further, what if one of those 60 million had a descendant who developed an early cure for the 2006 Avian Flu Pandemic?
Such thoughts boggle the mind ... how many seemingly insignificant events will happen today that will forever alter human history?