In my opinion, one of the best arguments for single payer in health care is that innovation and new businesses and job creation are stifled when people feel tied to safe jobs in big organizations by their medical insurance (if by "best argument" you mean the one most likely to convince the person who disagrees).
Similarly, I've watched talented friends of both genders (but more often women) get stuck in their careers because a workplace is "family friendly." The current organization offers good benefits or a flexible work schedule, so even though these association professionals need to move on in order to advance in their careers, they can't manage to leave.
What if the new place won't cover their kids' health care? What if they lose the schedule flexibility that allows them to manage child care changes without huge hassles with management?
The fact that they're stuck for years in jobs with no possibility of further advancement becomes the price of having a life that works. And that sucks.
It's a form of mommy-tracking, but it's even more subtle and hard to address than old skool "we don't promote mothers or give them big responsibilities" because it's, at least on the surface, a voluntary choice. Those handcuffs may be made of gold, but they're still handcuffs.
The thing is, "family friendly" policies like flexible schedules and good health care and reasonable leave policies have been PROVEN to increase retention (and we all know how expensive and time-consuming staff turnover is), improve the ability to recruit the best candidates, increase productivity and decrease absenteeism. The #1 reason people leave jobs is bad management. Treating your staff as less than equally valuable to senior management is pretty much the definition of bad management.
So what's holding us back?