So if Social Security (and don't forget Medicare it's part of the same FICA taxation) were to go away, it definitely means some nasty calamity happened first, like Yellowstone or a meteor just blew up half the country, in which case we've got other problems.
The thing to be concerned about is privatizing it. That's a con game to dump a shit ton of money into the stock market, with the ensuing distortion inflating the stock prices of the very wealthy. It's about helping them. It doesn't do squat to help the people who will depend on Social Security. They will not make more money. And just like with getting rid of it, there's no way it's tenable to tolerate the inevitable short term loss of asset value with recessions. We can't have retirees experiencing 5% let alone 20% loss of income for 1 month let alone 1 year let alone 5-8 years for a recovery. Old people would sooner pick up axes and make you shoot them, because shooting your grandma in the head is kinder than this Republican privatization of Social Security nonsense. Grandma is not going to go back to dumpster diving and living under a bridge again like the 1930's.
And you've got the same financial concern with an unbalanced 401K - that could leave you in a lurch the same way a privatized Social Security plan can. So take the risks in that 401k while you're young, but at some point probably in your 50's, you'll want to start moving it to inflation indexed treasuries.
Young people right now are more likely to be savers, because of 2007/2008. They saw what it did to the unprepared, so they know that sort of thing can happen. Gen X and the Baby Boomers didn't have anything nearly that scary.