Tell computer manufacturers that you dislike the concept of restricted boot and will not purchase a device that removes user's freedoms.

http://www.fsf.org/campaigns/secure-boot-vs-restricted-boot/statement

We, the undersigned, urge all computer makers implementing UEFI's so-called "Secure Boot" to do it in a way that allows free software operating systems to be installed. To respect user freedom and truly protect user security, manufacturers must either allow computer owners to disable the boot restrictions, or provide a sure-fire way for them to install and run a free software operating system of their choice. We commit that we will neither purchase nor recommend computers that strip users of this critical freedom, and we will actively urge people in our communities to avoid such jailed systems.

Edit: The FSF webpage might return some errors. It should work now, however if you do get any errors you can send your name and email directly to webmaster@fsf.org.