When Did Laws Prohibiting Same-Sex Marriage Become Unconstitutional?

At the oral argument today in Hollingsworth v. Perry, Justice Scalia repeatedly questioned Ted Olson on when same-sex marriage became unconstitutional. From the transcript:

JUSTICE SCALIA: I’m curious, when -­ when did — when did it become unconstitutional to exclude homosexual couples from marriage? 1791? 1868, when the Fourteenth Amendment was adopted? Sometimes — some time after Baker, where we said it didn’t even raise a substantial Federal question? When — when — when did the law become this?

MR. OLSON: When — may I answer this in the form of a rhetorical question? When did it become unconstitutional to prohibit interracial marriages? When did it become unconstitutional to assign children to separate schools.

JUSTICE SCALIA: It’s an easy question, I think, for that one. At — at the time that the Equal Protection Clause was adopted. That’s absolutely true. But don’t give me a question to my question. When do you think it became
unconstitutional? Has it always been unconstitutional? . . .

MR. OLSON: It was constitutional when we -­as a culture determined that sexual orientation is a characteristic of individuals that they cannot control, and that that -­

JUSTICE SCALIA: I see. When did that happen? When did that happen?

MR. OLSON: There’s no specific date in time. This is an evolutionary cycle.

Olson wasn’t inclined to give an specific date or window of dates in response to Justice Scalia’s question. But VC readers have: Results of the VC reader poll from 2010 on when same-sex marriage became unconstitutional (at least among those who think it is currently unconstitutional) is available here.