Yellow states have already legalized same-sex marriage. Purple states have not. Each state bubble is sized according to the estimated economic impact of legalizing same-sex marriage there. Williams Institute, Credit Suisse

Same-sex couples barred from marriage are also blocked — or at least discouraged — from spending all the money that weddings demand. They don't spend on marriage licenses, catering, reception venues, flower bouquets, or hotel blocks for their out-of-town guests. And the money they don't spend on all these things doesn't generate tax revenue either.

For this reason, states that have legalized same-sex marriage have made a lot of money off of that civil-rights progress. An early estimate of the economic impact of same-sex marriage in California calculated that some 50,000 in-state gay couples stood to spend nearly $400 million over the first three years of legalization — yielding $31 million in local tax revenue.

Multiply that effect nationwide, and the economic impact of gay marriage for local businesses and tax coffers approaches billions of dollars.

The Williams Institute at the UCLA School of Law has been estimating this same-sex marriage economic benefit in states across the country. Its latest estimate, neatly visualized in a new interactive built with Credit Suisse, calculates that state economies would collectively gain $2.62 billion over three years in a hypothetical world where all 50 states and the District of Columbia legalize same-sex marriage.

The bulk of that sum comes from the big states that have already done so: California, New York, Massachusetts, Pennsylvania, Illinois and Washington. But we still haven't tapped about 29 percent of the potential nationwide economic impact of same-sex marriage thanks to those states — primarily in the South — where same-sex marriage is still banned.

By the Williams Institute's estimate, Texas would likely see about 23,000 same-sex marriages in the first three years of legalization, resulting in about $180 million in spending and $15 million in tax revenue. Florida is missing out on a roughly equal windfall.

These numbers, based on the Williams Institute's earlier research, Census demographic data and wedding industry spending data, are imprecise estimates. And they don't take into account same-sex marriages that occur across states lines (so Pennsylvania, for instance, may actually stand to lose a little business in the real world when neighboring Ohio starts to offer its own same-sex marriages). It's also likely that some couples who can't legally marry still spend comparable sums on commitment ceremonies.

So take these numbers — which you can play with here — with a bit of caution. But they reinforce the common refrain that civil-rights policies of moral imperative often entail an economic boon, too.