As abortion opponents are scoring a string of victories in the states, it raises a question: why are conservatives gaining ground in this one arena, even if they're losing in the battle over gay marriage and marijuana?

A few factors help explain this contradiction.

The passage of new abortion laws comes despite the fact that public opinion has been stagnant - and mostly supportive - of the right to legal abortion since the 1990s. Fifty-five percent of respondents said abortion should be legal in all or most cases in an August 2012 Washington Post-Kaiser Family Foundation poll, with just over four in 10 (42 percent) saying it should be illegal in all or most cases. That poll result is smack in the middle of where support for legal abortion has stood over the past decade, seesawing within a narrow band of 53 to 57 percent in Washington Post-ABC News polls.

By contrast, attitudes on same-sex marriage -- and to some extent, marijuana legalization -- have shifted rapidly in the past decade. Last month, 58 percent of respondents in a Washington Post-ABC News poll said it should be legal for gay and lesbian couples to marry, up from 37 percent in 2003.

And that same month, 52 percent said marijuana should be made legal in a Pew Research Center poll, up from the long-term trend in General Social Surveys.

The data show that while there are big generational gaps in support for marijuana and gay marriage, there are fewer-- and shrinking -- differences between younger and older Americans on abortion. In 2012, 53 percent of 18- to 29-year-olds said abortion should be legal in all or most cases, compared with 50 percent of Americans 65 and older. In 2004 there was a 12-point gap in support between the youngest and oldest age groups. As a result, overall abortion opinions do not appear likely to shift much when the youngest generation replaces the oldest.

But on gay marriage and marijuana, the generational divide is enormous, and is part of what has been driving the shift in public opinion. Eighty-one percent of 18- to 29-year-olds said gay marriage should be legal in the March Post-ABC poll, compared with 44 percent of those ages 65 and older. And In the Pew Research Center’s marijuana poll, 65 percent of Millennials (ages 18-32) favored legalization, as opposed to 32 percent of those in the silent generation (ages 68 and over).

New abortion laws may also reflect the fact that while a consistent majority backs legal abortion in most or all cases, support ranges widely depending on the reason and timing of the procedure. A December Gallup poll found roughly six in 10 saying abortion should be legal in the first three months of pregnancy, but support plummeted for abortion in the second or third trimesters (27 and 14 percent, respectively).

And while the 2012 wave of the General Social Survey found overwhelming support for abortion in the case of danger to the mother's health, rape or a chance of serious defect to the baby, majorities opposed allowing abortion "for any reason" or if the mother simply didn't want another child.

At the same time, both liberals and conservatives agree that popular culture has embraced the concept of gay rights in the past few years, while abortion has largely receded from public view. The 1982 movie "Fast Times at Ridgemont High" showed a high schooler getting an abortion. Now, Tom McClusky, senior vice president for government affairs at the Family Research Center, noted that "even on soap operas you don't see an abortion."

Michael Cole-Schwartz, a spokesman for the Human Rights Campaign, a gay rights group, observed that marriage is, at its core, a public expression of one's commitment to another person, while abortions tend to be private decisions. While those who support and oppose abortion speak out on the issue often, women who actually undergo the procedure often consider it as a personal matter and are less likely to talk in public about their experiences.

And Cole-Schwartz noted that gay rights groups have yet to gain the same level of momentum when it comes to non-discrimination laws on either the federal or state level.

"Marriage is not the be all and end all of our movement, but it's the issue that's captured the public's attention," he said.

In fact, gays still lack the constitutional protections the Supreme Court awarded abortion providers and their clients 40 years ago. It is still legal in 34 states to fire employees based on their gender identity, and in 29 states to terminate them based on their sexual orientation.

Louise Melling, who directs the ACLU's Center for Liberty, said the gay and reproductive rights movements are "at radically different historic moments, which is what accounts for the difference... And at the end of the day, abortion is subject to restrictions, but it's legal."

To some extent, the publicity surrounding the Supreme Court oral arguments on same-sex marriage may have given the public a skewed sense of how much ground gay rights activists have gained in recent years.

"They were greeting each other and saying 'Happy Marriage Day,'" said Andrea Lafferty, president of the Traditional Values Coalition and an opponent of same-sex marriage. "The debate's far from over.".

Capital Insight survey research analyst Scott Clement contributed to this report.