Now, _will_ I do that? Probably not, but my opinion is that as the owner of the device, I should have the ability to do so if I so choose.
And what about the manufacturer? Why should it be their legal responsibility to satisfy your whims for programmable interfaces?
Not to mention what you're mentioning that what you're suggesting will make the iPhone incredibly insecure.
Regarding security, that very much depends on your threat model and definition of "secure". Indeed, I see this general trend of decreasing user control over increasingly complex and connected hardware as a massive security threat where I am forced to trust multiple 3rd parties who may arbitrarily disrupt my life anytime new "features" or "policies" get pushed out.
It is perfectly possible to securely implement a tamper-evident "I know what I'm doing" switch/fuse that enables advanced control by device owners. However, I'm well aware that I'm in the minority on this topic, so I'm not holding my breath for such features to be implemented.
That said, I doubt washing machine microcontrollers use signed code. It's easier to modify them than your phone which is completely backwards.
Yes. It is within my full legal right to install whatever programs I want on my washing machine.
Apple lost a bunch of lawsuits, when it tried to sue people for doing this. The courts proved that yes, you do have a legal right to do whatever you want with hardware that you own.
That's what Apple is doing here. Pushing iPhone as a commodity, not a replacement for your macbook. This way they get the benefits of controlling the experience as much as they want. (I am not saying it is right or wrong, just that many people are fine with commodity phones and don't care for the loss of configurability).