Why should I invest in Index Funds?

This weekend, hopefully, our Finance professor will tell us what's wrong with investing in Mutual Funds and why we should invest in Index Funds.  Why would we settle for market returns if we can safely beat the market?

Above, from Morningstar, you can see the first 50 actively managed mutual funds that have beat the S&P 500 over the last 15 years, as well as the last 10 years, as well as the last 5 years, and 3 years, and 12 months, and even over the past 3 months, and that also have a Beta <= 1!  This is a very tough requirement, but as you can see, there are 219 funds that have done that well.