I don't think it's unreasonable for a device manufacturer to tightly couple it to the software they design to run on it.

No Universal Machine, as a component or the whole product, which prevents owner modification through DMCA-styled digital locking mechanisms, must be allowed to be sold on the open market. Such contravenes the rights of ordinary citizens. It is disgusting to me that we have allowed this state of affairs through our collective and individual inaction. America's founding fathers (terrorists by today's definitions) tarred and feathered for much less!

That might be reasonable for a general purpose computer if we were talking about something like a Parallel Inference Machine running KL1 software on a KL0 kernel. But I think conflating Apple's products with that level of foundational engineering is highly disingenuous. They're not exactly trundling into the dark woods of exotic hardware and reinventing the bridge between human and computer. It's an ARM computer running a Unix clone. Apple's engineers aren't mapping every codepath and counting every micro-op, Darwin contains extensive amounts of third-party code.

Hardware and software have to interface at some point. When the people designing the hardware work at the company designing the software it's not unreasonable for them to come to some shared understanding of that interface which may not be standard, portable, or even publicly documented, and certainly not one that is stable.

This isn't incompatible with allowing users to install their own software. There just isn't an obligation on the original designers to make sure that software works. That onus is on the designers of that software.