No, they're trying to make sure they get their pound of flesh any time one of 'their' devices needs to be repaired. If the NSA (et al) are really serious about having hooks into Apple products they'll make sure to get them [1], glued screens and batteries and firmware kill-switches notwithstanding.

If it were about privacy and security Apple could have the device display a warning when it detected tampering and leave it to the user how to act on this, a bit like some Android devices react when the bootloader is unlocked. They could also sell OEM spare parts which could be used by third-party repair shops to repair devices and use a verification routine to re-certify the device (which then would not display a 'tampered' warning, instead showing a 'repair log' in some hidden settings screen).

[1] https://en.wikipedia.org/wiki/PRISM_(surveillance_program)

Pound of flesh? They're offering battery replacements at $29. That's probably a loss leader since it's 30 min of labor plus parts.

They only started offering it at that price after great public outcry when it was exposed they were purposefully slowing down older devices..

...in order to allow them to continue to run.

C'mon, at least finish the damn sentence. They were slowing down older devices to make sure that they wouldn't just literally shut down when the aging battery could no longer supply enough power for spikes of usage.

..by the new OS/kernel they forced you to install, without writing it to be friendly to the old phones they're forcing it onto.

Forced you to install?? No one forced you to install the newest version of iOS.

Do Apple keep security updates over the old versions? That could be an easy way to be forced to update.

Theses 2 relatively recents vulnerabilities are pretty good reason to have to update. https://www.krackattacks.com/ https://www.armis.com/blueborne/

I doubt that state actors would find it much of a hindrance; they could route targeted phones through Apple-approved repair organisations for modification.

it's to prevent chop-shop theft.

Yes, because taking one of their repair kits would be naught impossible?

The technique has nothing to do with security.

It's pretty obvious when an iPhone X is repaired. Apple's strict stance on security means it's not impossible that this was done for security.

A kill-switch on unauthorized modifications has a massive positive impact for device security.