> Most computers in the world don't need the ability to have their operating system changed or run custom user built software.

That's not true? Nearly every laptop, desktop, and server can trivially run whatever OS+software, of course, but also currently at least virtually all Android devices can run arbitrary user built/supplied software (I grant that, unfortunately, replacing the OS is often harder). Embedded stuff varies, but frequently anything capable of running a general purpose OS (which IMHO is generally the line to call it a "computer") can have it replaced.

I HATE this argument. If the PC had been locked down like smartphones are today, we would never have had Linux on the desktop.

Also, replace "consumers" by "people" who might need to control their devices to do things that may be against the interests of the manufacturer, like removing ads and surveillance.

If consumers are fine with the pre-existing software and will never try to use anything else, why do we lock them out though?

Something doesn't add up.