For example, it seems after slavery we progressed to ending segregation, allowing interracial marriage, outlawing workplace discrimination, etc. Today, only a small minority would still agree that those against slavery were wrong. Women seem to be progressing in gaining rights similarly and very few would say they "belong in the kitchen."
For context, I'm curious about those adamantly opposed to gay marriage. In a matter of years, won't the majority of Americans support LGBT rights and gay marriage as it becomes the norm? And is it the case in the U.S. that those opposed to any specific group of people gaining more rights or equality typically do end up "on the wrong side of history?"
I really can't think of an example where this happened (i.e. most people don't think, "damn should have never given the disabled accessible parking," etc.
-Also I'm not trying to debate the ruling, I'm just wondering about historical precedent - thanks!
Well the most obvious case would be in the Reconstruction Era South, in which African American men were allowed to vote, and combined with other Reconstruction Era restrictions on former Confederate actually allowed several Freedmen become members of Congress. With the end of Reconstruction and the reassertion of southern, conservative, white control, those rights were reduced and effectively eliminated until the Civil Rights movement and the Voting Rights Act, the latter of which has seen its own revisions in the recent past that I won't get into because of this sub's rules.
So that would be one example that sort of fits your question. Another that sort of (but not really) fits would be the rights of women during Revolutionary France. Several historians have argued that women gained rights under revolutionary governments that were later rescinded under Napoleon. Similarly, the Revolutionaries freed the slaves in Saint-Domingue, only to have Napoleon attempt to re-institute slavery later - he failed.
In both cases though, I think you'll notice that they are not permanent regressions. I once had a scholar of gender studies suggest to me that instead of seeing these things (in this case the person was discussing "society's" attitude about the LGBT community), it's probably better to think of external attitudes as ebbing and flowing instead of being a pure progression or regression - it's two steps forward, one step back.