Exchange traded funds (ETFs) continue to spark a hot debate. John Bogle, Vanguard Group index founder, is crusading again. This time he is defending traditional index funds that are based on market-capitalization. On the other side, Robert Arnott, chairman of Research Affiliates and "Godfather" of fundamental indexing, says classic indexes can use improvement, says CNN

Bogle’s approach is if it ain’t broke, don’t fix it. The main argument for fundamental indexers is that a market-capitalization weighted index is not a true indicator of success because it tends to tilt in favor of already over-valued companies. Arnott says efficient markets and market-cap weighting are inseparable; however, he aims to "weight companies by what they own and produce, and mirror the evolution of the economy."

Bogle may see fundamental indexers and ETFs as an attack on his legacy; however, many of the new breed say it’s an evolution of his legacy. Industry insiders have lots of respect for Bogle and his revolution within the mutual fund industry. Bogle wants investors to know, whenever there’s a hot, new product, "Zip up your wallet."  We at ETF Trends say, "Please don’t zip up your mind!"

The opinions and forecasts expressed herein are solely those of Tom Lydon, and may not actually come to pass. Information on this site should not be used or construed as an offer to sell, a solicitation of an offer to buy, or a recommendation for any product.