The Argument For the Efficiency Market Theory

1. The bottomline of Efficient Market Theory (EMT) is that you should invest in low cost index funds. I could never fault someone who takes that approach. My 401k is invested in indices. The world is a better place with John Bogle in it and Warren Buffett himself recommends index funds for investors who don't want the hassle of picking stocks.
2. It would be foolish to think of the market as totally irrational. Otherwise, prices would be random. All parties pretty much agree that the market is, at the very least, mostly efficient. The theory, therefore, applies to that part of the market that everyone agrees is efficient. Thus, the EMT has some value as a predictive model.
   
3. EMT says that market timing, charting and momentum investing are poor investment strategies. They are.
   
4. Pension fund and endowment managers have other concerns besides pure performance. Due to the need for steady income as well as appeasement of leadership and beneficiaries, rejection of risk, as classically defined by EMT, may not be an option.
   
5. Even if you don't believe in it, your bosses might.
   
6. Most important, the more EMT is taught in schools, the more easily it is for value investors to find mis-priced securities. =)