There's a lot of writing and history behind open source, open firmware and even open hardware, but the BIGGEST thing you can focus on is the transition from PCs to smartphones around the 2000s.

We went from you installing whatever boot loader and operating system that could run on your device, to a locked down boot loader that would only load the vendors operating system.

They hide behind security through obscurity, but it's been debunked. The boot loader and even firmwares of devices have in certain cases been found to be gushing gashes of CVEs and bad coding - but only through decompilation and reverse engineering. In fact, after the 5 year warranty of your device is up, you should consider the security of your device highly suspect.

The true purpose for an exclusive locked down boot loader is to maintain operating system monopoly, force uninstallable apps/services on a user, to then be able to track & canvas the user to sell on the data brokerage market - not to mention planned obsolescence, because if you can't freely modify and update your firmware and/or boatloader, you could secure it for more than 5 years.

For a more balanced take and to see "both sides", read this

Other than that, the LibreBoot mailing list will help you to unearth the hypocrisy and lies fed to us by hardware vendors.

Free the firmware, free the bootloader, free the operating system, free the drivers, free the software - and then the user can decide wether or not they want to run commercial software on top of all this.

Anything else is subservience.