I'm not sure which of Roger's articles you're referring to, but if it was the one linked above you need to read it again, hopefully you'll comprehend it this time.
No where does he mention focal reducers or speedboosters. In the opening he mentions, "One thing that has always bothered me, though, is the idea of doubling the number of lens-mount interfaces." He's not talking about adapters with optics, he's talking about tube adapters like the Nikon to NEX (he has Novoflex), Canon EF to NEX (he has Sony), etc. No glass in those, just air. He's talking about the effects of misalignment of the mount interfaces.
Agreed that the problems are evident with wide lenses, not telephoto. But that just further supports my point that the argument that adapters are not a problem because no one complains about teleconverters is a fallacious one.