Yes, unlike Social Security it's legally your money. You can will it to others when you die. You can access it while you're alive, albeit at a penalty partly to offset the fact your investments were made tax-free to begin with.

And yes, depending on your employer, you might get the money as wages instead of as a match. You could certainly negotiate for that. Try doing that with Social Security.

You don't have to invest your 401ks in the stock market and, no, the stock market is not a Ponzi schema, unless you're just redefining Ponzi scheme to mean something else.

Anything else?