Even if you save up the money to not be desperate in these situations they still have a very high cost. Say you’re 30 and invest in a big index mutual fund. Having to use these funds means shaving 8x as many months off your retirement.
1. Those 401K's and IRA's have a yearly cap, so anything above that cap doesn't apply. 2. Saving your "rainy day" account is a one time thing. Once you reach 4-6 months of income, you are done. 3. Like we agree, you can put it in a non-tax sheltered fund.
Also, not sure if you are going to get 8x return in 30 years. Maybe 50 years ago. When I was in college you could expect to double your money ever 7 years. I don't believe that's still the case.