he's basically using an argument from authority "phd's say"
why CARES who is saying it? the issue is the theory, not its pedigree
academics are frequently wrong , and this is ESPECIALLY true in "soft sciences" like econ and social work, etc.
i gave already several examples of academic rubbish being peer reviewed and supported for DECADES despite immense contrary evidence.
proponents of EMT use the same illogic that many intelligent design people do- as regards to "provability" etc.
cause if somebody is a successful trader, they are just discounted as a random aberration.
but when i personally (and have seen my mentor and others) CONSISTENTLY reap profits from the market, it is clearly not efficient to the extent that edges cannot be developed
for example...
in the 90's bull market, one edge was pretty simple. emphasize growth over value, and buy strength (generally speaking).
now, we are in a means reversion low volatility market environment
why?
because the market IS what people are doing, therefore it adapts to their changed behavior. now that that edge is thoroughyl disseminated and used, it ceased to (generally) exist, and the market moved into a phase where mean reversion is the better strategy (generally speaking)
most of my futures trading strategies involve mean reversion concepts, because that is what works NOW. and a lot of the reason they work is that i know how most retail traders trade (using lagging indicators like MACD, RSI, etc.) with a healthy dose of emotion, panic, fear, euphoria, and chasing to go along with it.
so, part of my edge is NOT trading that way, but being peripherally aware of what the loser trader is doing
as for the comment about if i buy, somebody sold therefore they didn't think it would go up. that is less true with commodities (and some futures) than it is with stocks
the reason is that a large part of futures volume (especially in ags) is done by commercials hedging. if i own 100,000 bushels of corn to go to the market in Dec., i will short corn futures. im not selling futes because i PREDICT the market will go down, i am selling because it offsets my physical holdings and leaves me market neutral. consumers do the opposite by going long what they want delivered in the future, to counteract price rises
so, one can look at COT reports, institutional capping reports (CBOT provides these) and understand the nature of many commodities markets to also have an edge. in that case, you are not outtrading the commercials, you are understanding their footprints and taking advantage of the movements