When new parents in America decide how much time to take off work to spend with their newborn, the factor that usually matters most is their job. And for two-thirds of Americans, the amount of paid family leave their job offers is none at all.

Paid leave for new parents is a rarity in the United States—the only industrialized nation that doesn't require it for new moms. Some states, including California, New Jersey, New York and Rhode Island, guarantee most new parents some paid time off. But despite strong support in both parties, a nationwide law seems far behind.

Alexis Ohanian wants to change that. The venture capitalist was vocal about taking off the full 16 paid weeks available to him when Alexis Olympia, his daughter with Serena Williams, was born.

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"It was immediately after the birth of Olympia and all the complications that my wife went though that I really understood how much of a difference it makes," he told CBS News this week.

"I could not imagine a dad having to make the decision about going back to work or being there for their partner or for their child," he said.

Ohanian was in New York this week to launch a campaign championing parental leave with Dove Men+Care, which aims to give away 200 grants of $5,000 apiece to expecting fathers who otherwise couldn't take paternity leave. He also said he will lobby Congress later this year to pass a federal leave law.

"For a country that purports to care about families as much as the United States says it does, this is a no-brainer," he said.

Other rich and famous fathers, including Facebook CEO Mark Zuckerberg, have also made it a point to publicly take extended leave when their children were born. Such high-profile demonstrations from the top 1 percent of professionals can start to shift expectations for regular working fathers, the vast majority of whom take less than two weeks off when their child is born, even when time off is available.

"The imprimatur of the leader, to say 'it's okay to take it,' is important," said Jocelyn Frye, a senior fellow at the Center for American Progress. "A lot of times people retreat to their cultural norms, and even if [paid leave] is available, men may think it's not okay to take it."

An Urban Institute study found that nearly all working fathers believe "their supervisor expects no change to occur to their working patterns as the result of their becoming parents."

Ohanian thinks he became a more efficient worker after becoming a dad. "One more reason that I think people end up getting better at work after having kids is you find ways to cut out things in your life that don't matter as much," he said. "You start to prioritize things."

Research shows that being more generous with paid leave for all workers actually reduces the burden on women, who are still the primary caregivers in many societies. The leaders in this field are Sweden, Denmark and Iceland, all of which have ample family leave policies—and require that it be shared between a mother and father. That's shifting the division of labor in families so that both men and women contribute equally to the workforce.

These countries are updating their family leave laws, on the books since the 1970s, to account for same-sex families.

Stateside, New Jersey recently expanded its paid leave law to account for that, making the benefit available to all people in family-like relationships, even those who may not be related.

In that sense, family leave is a purely economic problem. In the U.S., nearly half the population is unable to contribute to the economy and civic life because the demands of caring for children or family members, unpaid. The expectation that private businesses will take up the slack hurts small employers in particular, many of whom can't afford to offer their workers paid leave even if they want to.

Polls consistently show overwhelming support among Americans for the policy, even across party lines. A recent poll showed 94 percent of Democrats and 74 percent of Republicans support a national paid leave policy. Both Democrats and Republicans have introduced paid family leave laws in the current Congress.

"The real question is, what will it look like?" said Frye. "Unless you have a comprehensive approach, you risk doing more harm than good. If you have a program that singles out one group you foster resentment and cause employers to single those folks out."