Earlier quoted context omitted.
If the Efficient Markets Hypothesis (in its stronger forms) is false, there should be managers who are able to identify the cheapest stocks within the S&P 500 and thereby outperform the index. A disbeliever in EMH should look to identify these managers and pay them some fee, rather than simply investing in the index and trying to minimize fees. I think it's plausible that these managers exist, but they're impossible…
You say "A disbeliever in EMH should look to identify these managers and pay them some fee". In the next breath you say that even if the EMH is false "individuals investors should act as if it were true". This makes your post somewhat ambiguous; not so clear about which position you're advocating. How "plausible" is it that these managers are "impossible to identify ex ante."? Why is it plausible? "Impossible" seems…
(And yes, I understand that you agree with the conclusion there. But I'm saying what's the point of the verbal gymnastics in the first place?)