401K makes you getting RICH or retire faster.

I don't think there should be any arguments to discuss 401K is good or not.

Let's calculate this way:
1. Assume you are 30 years old, you need 30 years to retire at 60. You are in 40% tax bracket(fed+state).
2. Assume 10% gain each year, 3% inflation.
3. Assume you have $1M in your 401k this year, or $600k cash (after tax $$), but not both.
4. In 30 years, your 401K money will grow by 1.10^30 = 17.45x. The 3% inflation factor 1.03^30 = 2.43x. So your real money at 401K will be $1M * 17.45 / 2.43 = $7.18M
5. The same calculation applied to your $600K after tax money. Since you have to pay 40% tax for your 10% gain each year which reduces your annual after tax gain to 6%. So your money will grow by 1.06^30=5.74x, inflation factor 2.43x, then you will only have $600K * 5.74/2.43 = $1.42M.
6. At the end of 30-year period, you will either have $7.18M in your 401K account, or have $1.42M in your cash account, unfortunately not both. All these money has been converted to current money after inflation.
7. Assume you have 50% tax bracket for your big 401K account when you retire after 30 years, you withdraw all your gain (10% of $7.18M) each year, you will still have $360K to spend while your principal still keeps at $7.18M in your 401k account. In contrast, if you take all you 10% gain from your $1.42M cash account, you can only have at most $142K to spend even no paying tax.

Similar calculation can be done for lower/higher tax brackets. In one word: 401K makes you getting rich or retire faster!