@7 Loving did change the definition of marriage in the dozen or so states that forbade interracial marriage. And at the time it was passed, the majority of American opposed interracial marriages.
To quote Gallup:
"When Gallup first asked about black-white marriages in 1958, 4% approved. More Americans disapproved than approved until 1983, and approval did not exceed the majority level until 1997."
Support for interracial marriage is now around 86%. Marriage equality is following the same track. In 1996, it was 27% pro/68% against. It's now 51% pro/48% against. And in both cases, those opposed are concentrated in older age groups. As they die off the number continue to shift.
Conversely, opinions on abortion haven't budged in 40 years. In 1975, it was 27% always legal/54% sometimes legal/22% never legal. In 2012, it was 28%/52%/18%. Those differences are fairly stable and fairly durable.
Roe v. Wade is a poor analogy.