What if lockdown worked in such a way that you could lock it down to only run your Linux kernels? E.g. load up your own certificate in the TPM and use that for signing when you build.

In that case it would be a security feature -- another line of defense against bootloader malware and/or adversaries in physical possession of your machine.

(I don't know how technically feasible that is; I know Canonical and others are looking at having their own cert so at least their unmodified kernels can run, but I don't know the mechanism for how that interacts with already-released UEFI machines.)

The point is that technologies like this are a double-edged sword, not evil in themselves. A similar argument is made by Linus himself for sticking with GPL v2 instead of moving to GPL v3, which outlaws certain DRM-related uses; he's more interested in providing a functioning mechanism, and leaving the policy-setting to others.