If you might need the money, how is donating it to Wall Street through day trading on -EV plays somehow better?
If you might need the money, it needs to be somewhere safe like a savings account or a CD. Once you have an emergency fund, you can start saving in higer-risk/higher-reward +EV investments like index funds.
Positive expected value is positive expected value. This works great, as long as you have plenty of bankroll and can ride out any losses.
As you say, this advice doesn't apply to people who might need the money.