> But at least in theory what Wall Street is selling you here is better return than what you could make on an index fund.

Often, 401k's offer few, if any, index funds and at drastically higher fees, even if the fees are lower than actively-managed funds.

To take a personal example, I have retirement accounts with Vanguard (Roth IRA), T. Rowe Price (solo 401k) and, through my employer, with MassMutual. All offer an S&P 500 index fund, but Vanguard's fee is 5 basis points (.05%), TRP's is 30 basis points, and MM's is 90(!). Why am I paying almost 20 times as much in fees through my employer?

Sure, you could put this back on my employer and say, "well, they should offer you a 401k with better options/lower fees/with a better vendor," and though I'd agree, it's not as though I have any say in the matter, which is the point that Bogle and Frontline are making.