Ok, so how you would write this (at least the first section, explaining the error) constructively could be much shorter.

"The author of that post has a common misconception, which is that spin locks are a fast drop in replacement for uncontended mutexes. They aren't. You can only use them well when you know you won't be descheduled, like we do in the kernel. In a generic userspace program, you don't have that knowledge. The possibility of your time slice ending skews all the time measurements, for example."

Boom. Roughly the same message. Most people will get the same amount of edification from this as Linus' original letter. You could go in to more detail if you want but it's not really necessary. Smart people will figure it out if you just point out the general shape of the error. No need for calling code "garbage."