It isn't more unreasonable or indeed any more illegal than Apple refusing to support Adobe's Flash Runtime on their platform. And this only affects Windows certification not the underlying principle of a PC as an open platform. Since UEFI standard is modular, it is simply a matter for the OEM to provide a secure environment module, which the end user can choose to use or not, depending on requirements. Linux will adapt as it always did.
Furthermore, multi-booting in the age of virtualization is somewhat of a basket case scenario.
