I think it's important to point out that the conclusions are definitely still the same despite the lowering of trading costs since 2000.
Trading is hazardous to your wealth, period.
Trading is hazardous to your wealth, period.
Most of the reported difference in net performance is due to the impact of commissions and spreads: As trading goes up, gross return was not impacted, but net return was.
Retail investors in 2000 were getting fleeced. (And if you think that's bad, take a look at commissions in 1980.)