The best complexion to put on this is that Apple engineers had our best interests in mind. Many kinds of software and hardware can tell when an intruder has been at work, often when hardware has been tinkered with. For instance, secure flash drives - like these from Verbatim - have often featured internal mechanisms that permanently disable a drive if someone tampers with the circuitry or tries to remove storage chips. You can buy tamper-resistant hard drives, computers and, yes, smartphones.
In some industries and for some people, buying a device that kills itself rather than gives up its secrets - or even allows the potential for a third-party to grab the data for later analysis without revealing themselves - is desirable or required.
The classic man-in-the-middle (MitM) attack, which is a constant threat for online communication, can be mitigated by providing a means for Alice and Bob, the typical ends of a conversation, to detect when Eve butts in. In PGP, for instance, the intertwined public and private key pairs used to encrypt data can be verified outside of an interchange to be sure that nobody tampered with a message en route. PGP is used in making digital certificates with third-party verification in browsers and operating systems, so that when you connect to a server, you have assurance that an Eve hasn't set up shop between you and the server.
In this case, Apple seems to have made a perfectly reasonable engineering choice: it's better to brick a phone than to potentially allow someone's phone, payment or other data be used by another party. In practice, it's overkill, as many perfectly reasonable engineering choices often are.
Those who have long criticised Apple's attitude towards owner and third-party repairs of its products - which have largely become more difficult over time due to components, assembly methods and specialised connectors and screws - denounced Error 53 as a way for Apple to both make more money and deter third-party repairs.
Apple will repair or completely replace a broken iPhone that's out of warranty for US$299 (6/6s) or US$329 (6 Plus/6s Plus) in the US, and keeps the old phone if it's replaced. Under its one-year warranty, such a replacement should be free, unless the damage is from an accident that the warranty doesn't cover. AppleCare+ covers such accidents, repairing or replacing the phone for US$79 (iPhone 6, 6 Plus and older) or US$99 (iPhone 6s and 6s Plus), up to two incidents across the three-year contract.
There's surely some profit in there, as Apple uses refurbished iPhones for replacements, and reports indicate it scavenges working parts from broken phones to use in refurbishing others.
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