NEW YORK (TheStreet) -- Irish voters are preparing to vote on the world's first constitutional referendum on legalizing same-sex marriage. The vote on the Marriage Equality Bill is set for Friday, with results due on Saturday. Irish lawmakers passed the bill in March. The vote will only affect the independent Republic of Ireland, not Northern Ireland.

While polls have indicated most voters are planning to approve the referendum, the margin over those who are planning to vote against it has narrowed. And Dr. Mark McCormack, a sociology professor at Durham University in England, warns watchers to be cautious about the polls, noting that surveys of voters ahead of the recent U.K. elections didn't reflect the outcome. 

What's interesting about the battle in McCormack's view is that it pits Prime Minister Enda Kenny against the Catholic Church, which has seen its influence in Ireland wane in recent years. The referendum, he said, will reveal more than just the population's opinion on gay marriage: It will signal who has more influence over the heavily Catholic Irish population -- the church or the state.

The referendum itself, he said, is part of a larger global trend.

"Obviously, we're seeing shifts in homophobia," said McCormack, "some certainly negative in some particularly African or Middle Eastern countries, but when you look at the West, there's a clear trend towards legalizing and approving of same-sex marriage."

Asked about the potential impact of this vote economically,McCormack demurred, noting that it was too early in the trend to quantify, but suggested that the "inclusivity" that a yes vote would signal might possibly attract more tourism to Ireland.

However, he also pointed out that a countrywide change such as Ireland is contemplating differs significantly from the state-by-state shift now happening in the U.S. 

In the U.S., he noted, some big companies and organizations have decided against doing business or hosting events in states will laws against same-sex marriage. On the other hand, some individual companies that have publicly taken stands against gay rights have been met with support from religious organizations and conservative consumers.

McCormack also thinks that legalization of same-sex marriage may also lead to the devaluation of what in the U.K. they call the "pink pound" -- the extra disposable income available to well-off gay consumers, who don't have child-rearing or marital expenses. If gay marriage becomes legal, he said, and the lifestyles of homosexual couples become more family-oriented, much of that previously "spare cash" might be redirected toward that. 

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