They can be but they're not. Once you share a wire all bets are off.

By that logic there's no security on the internet at all. Everything "shares a wire" after all.

Security is about degrees and nuances. These kind of black & white statements are unhelpful and unrealistic.

> By that logic there's no security on the internet at all.

Have you /been/ on the internet, lately? ;)

Two systems that accept input from the same touchscreen can't be isolated in hardware. From the software side, any portion of each system's interface that overlaps at the touchscreen cannot be isolated. On top of that, if the touchscreen is reprogrammable, then it can be attacked directly and touchscreens are commodity devices not normally considered part of the security infrastructure.

I don't think anybody is upset that their climate control system is exposed to hackers. There are no accelerator/steering/braking controls on the touchscreen (I assume) so those could be isolated but it would require having to separate systems for critical and non-critical operations. The only reason not to do that is because it's more complicated which translates to more expensive.

The climate control isn't mechanically independent of the engine and other mechanical systems. Even in the primitive cars before digital contols, the heater is dependent on the engine's thermostat (well except for old Bugs and 911's, but then that heat never really worked). In modern cars, the AC may be connected to the engine control system so that power can be redeployed for fuel efficiency or for power in emergency situations or to keep emissions within specification.

"Climate control system" is an abstraction over belt driven moving parts.

Exactly