The Free Software Foundation On SecureBoot

https://www.fsf.org/campaigns/secure-boot-vs-restricted-boot/whitepaper-web

We have been working hard the last several months to stop Restricted Boot, a major threat to user freedom, free software ideals, and free software adoption. Under the guise of security, a computer afflicted with Restricted Boot refuses to boot any operating systems other than the ones the computer distributor has approved in advance. Restricted Boot takes control of the computer away from the user and puts it in the hands of someone else.