As for the simple question why those who refuse to do a blind test/audition to me there could be a few reasons, and 2 come to mind, being afraid to chose the component that "is best", or being afraid to realize that your position on a subject, for example like you say you can(n’t) distinguish the difference in AC or Ethernet cables is wrong.
I have never bought a component without a blind test, my audio dealer facilitates that. All of his 6 audition rooms are set up for blind testing, all you need to say is I want to audition x,y,z he will also include one or 2 of his choice and then call you so you can audition until you have an ordered/ranking of the components you like best. If you tell him what components you have will will do his best to reproduce them so at the very least you have the reference.
I have walked out many time spending a lot less, and many others spending a lot more :)
The process is as long or short as you want, this is why to me blind auditioning is the best way to let my ears do the choice, and I have yet to walk away with a component that does measure great. As always, there are exceptions, like a PS audio powerplants, I know very well that will not do anything to my components' sound side because they are on the DC domain, but they are a nice looking power strip.