Wrong. It does prevent the kinds of malware and rootkits that operate by modifying the bootloader.
1) Whatever it does, it can be nullified by malware that gains root-level access AFTER the OS has booted (which is the norm). And if the malware managed to modify the bootloader, of course it has already gained that access, hence no effective protection is added, UNLESS you are running a machine that doesn't allow unsigned software to run (EXEs, batch scripts, stuff written by the user) that could have been installed or patched by the malware. But clearly this is not Windows as we know it today.
Moreover, locking down the machine (this is the only firmware behaviour authorized by Microsoft when the so-called Secure Boot restriction is violated) is arguably the worst outcome for desktop users, as they will be left with no way to service the machine (beyond running "rescue partitions" which of course are static and therefore can't contain anti-malware software), and with no access to their data.
2) Malware that operates by modifying the boot sequence is extremely rare today, because it must target specific hardware, and is associated with government-sponsored attacks. Of course, three-letter agencies are only a piece of paper away from having their malware signed with legitimate keys.
and harmful thing
Cite specifically the "harm".
Read the thread. I'm no parrot.
Well, now it's no longer true, as widely expected by the hysterical idiots.
And being hysterical idiots you and the rest of them still haven't figured out that in fact it is still true, in fact unless some OEM makes the choice to not include the ability to turn it off it will remain true.
"Unless" is they key word here.
Describe exactly how the OEM being responsible for their product is "anti-competitive, anti-consumer and anti-free software behaviour", because that does not make any sense in any context whatsoever.
Imagine that I am an operating system vendor and I want to sell an OS. Describe exactly what I have to tell my customers before I sell them my OS.
Imagine that I know an unskilled person (grandma) running an old version of Windows that is no longer supported on an otherwise perfectly fine machine. Describe exactly what I have to tell her before I propose to install Linux, or a commercial OS costing less than the new version of Windows, on her PC.
Imagine that I am a student and I've heard about this Linux thing. I'd like to try it on my PC that I bought off a shelf a couple years ago. Describe exactly what I should do to try Linux on my machine, fix it when it doesn't work and add new features to its kernel.