For those who haven't been paying attention, Apple and the FBI are currently in a fight over encryption on iPhones. To summarize: the FBI wants access to the San Bernardino shooter's iPhone, but needs Apple to create a “back door,” to do so, which could then theoretically be used to access every iPhone. Unfortunately, it's not as simple as giving the FBI a one-time key to one mass murderer's iPhone.
On last night's Last Week Tonight, John Oliver explained the issue at hand, as well as all the reasons why he thinks Apple is right to resist the FBI's request.
Basically, it amounts to opening up a can of worms far worse than the possibility that criminals will have protected communication with each other, which they'll just be able to do via a thousand other apps that the FBI can't control anyway. It could also compromise Apple's devices' security that much more in a world full of hackers looking for ways to exploit it.
Oliver explains this more eloquently than I can (and makes fun of that “rose gold” iPhone, which is worth the price of admission), so watch his 18-minute-long version below: