Explanation: The Catiline Conspiracy was an incident in which a Roman Senator, the titular Catiline, planned to overthrow the Republic by force. Cicero discovered this plot (not on his own), and in exposing it, contributed to the downfall of the conspiracy (though arguably it never really had a fighting chance). Cicero would proceed to not shut the fuck up about this for the rest of his political career, and oftentimes in Cicero's speeches you'll end with an aside along the lines of "And when I saved the Fatherland from Catiline..." A time-traveler who killed Catiline would doubtlessly spare countless future Latin and Classics students from having to read Cicero endlessly fellate himself over foiling the conspiracy!
Not a fan of the meme template but as an inversion I tolerate it.
Always happy to help out! I try to add context so everyone (who wants to) can appreciate the meme, not just the ones who already know about whatever minute trivia of Roman history is being memed about XD
Funny enough, one of Cato the Elder's opponents would end all of his speeches with "Carthage must be preserved" in response to Cato's "Carthage must be destroyed" spiels.
Secondary explanation: going to all seven games of the 1975 World Series would be a foolish use of time travel technology, because while you would get to see the Big Red Machine it would also require being inside '70s Fenway Park. It would be one thin notch above naked dumpster diving.