But isn't the risk of diversifying compensated by a corresponding possibility of large reward if the sector outperforms? I wouldn't consider a strategy that produces modest losses with high probability but large gains with low probability sufficient to disprove my claim.
Let's go one step back on this, because I think our point of disagreement is earlier than I thought in that last comment.
The efficient market hypothesis does not claim that the profit on all securities has the same expectation value. EMH-believers don't deny, for example, the empirically obvious fact that this expectation value is higher for insurances than for more predictable businesses. Also, you can always increase your risk and expected profit by leverage, i.e. by investing borrowed money.
This is because markets are risk-averse, so that on the same...
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