Subnormality/Fridge

Fridge Logic:

• In this comic, some time travelers try to prevent John Lennon from becoming a musician, so that he won't be eventually assassinated; and some other time travelers appear to stop the first group, so that the Beatles won't never exist. But why would any of them do any of this? Wouldn't it make more sense to go 20 years ahead and kidnap Lennon's murderer before he got a chance to do anything...? This idea isn't even brought up. In fact, the punchline is that at least two other sets of time travelers have already attempted the same thing, and apparently no time traveler ever tries the obvious solution, because if one had, the whole strip couldn't have happened. It's a good thing they decide to undo the invention of time travel, because they can't seem to figure out how to use it...