Just because you're buying "hardware" doesn't mean you're getting the privilege of installing whatever the hell you want on the device.
When I buy a Chevy Volt, I am not forced to fill up with only one vendor's gas. I am not forced to charge up with electricity from a particular utility.
When I buy a Sony TV, I am not forced to watch content only from Sony/Columbia/VEVO.
When I buy a Sansa MP3 player, I am not forced to buy and load only music from Sansa's "content partners." Hell, on many of their players, I can kick out their clunky UI and replace it with an entirely different clunky UI
There is no technological reason that a "Surface" tablet can't run Android or generic Linux. The only obstacle standing in the way is entirely gratuitous, malicious, and childish. To the extent SecureBoot improves platform security (it doesn't) or the integrity of the user's data (it doesn't), there is absolutely no reason that the root keys to such a regime be held by Microsoft, especially given their track record. SecureBoot is there solely as a very deliberate and calculated "Fsck you" to competing operating systems. Therefore, it is entirely correct and proper to call Microsoft out on it.