Mummert and others believe a lot of this ignorance started when Peterson Publishing decided they liked the small block scrubs and pushed them. Chevy was very busy making sure the aftermarket had access to their engines before public introduction and time to develop "Speed Equipment" for it. Ford on the other hand didn't seem to care. Even back then the average Joe would ask the gearheads about which car to buy. Chevy knew that (Duntov, Vince Piggens, etc) and used it. I think another thing that helped develop the "Y's are slow image" was the combination of the Loadamatics and the early Fordo's that started in second gear. Take a 272 two barrel Ford-o-matic in a Crown Vic and you have not got a race car. Although they sounded great with Smitty's, they were slow. By the time Ford responded, the damage to the Y block reputation was done. If you repeat a lie often enough, it becomes the truth.
Guys like Ted and Hoosier, JC. etc.etc, have proven that it was anything but the truth, but it's 50 years too late to help the Y.
You should see the stunned looks of the older crowd at the Pure Stock races when I show up with the red F code. 95% of them think it's either a 390 or something. They've never heard of an E code or F code Y block. Most won't believe it's stock, and even many of the guys my age, who were there when the cars were new, never heard of a 312. all they ever heard or read about was Scrub, Scrub, or Pontiac or Olds. Gonna be tough to change a 50 year old perception. I , personally don't even try, I mean who cares what the monkeys, who will never build anything, think? Those are the same guys who ran Tunnel Rams on the street because Bill Jenkins had one on his pro stock cars. 
Monkey see, monkey do.