That's called "Social Security" and the welfare system. It's a bit of a stretch (as in, take your 1970's Stretch Armstrong action figure and tie him the to the bumpers of two cars headed in opposite directions) to equate the idea of "a dude blows all his retirement money on crypto and we're going to bail him out" to "401(k) companies have a fiduciary responsibility to look out for their clients' best interests".

No one said we're going to "bail him out," in the sense of replacing all of his losses dollar per dollar. I'm simply pointing out that when if a person loses their retirement funds, some of that cost inevitably shifts to the broader society as long as social safety nets exist.

No one's arguing for a "bail out 401(k) idiots program." We're arguing for a "keep limits on what 401(k)'s can invest in so that it's less likely people will lose all their retirement savings." The same reason we require people to wear seatbelts when driving. We don't let them take the risk of being horribly injured in a crash, even if they're willing to take that risk, because we know that it will affect people other than just that one person if they get horribly injured.