It’s going to happen eventually. The only question is WHEN.

In 2009, Maine voters used a people’s veto to overturn the law giving gay and lesbian people the right to marry. In November 2012, marriage will be back on the ballot.

This is another occasion to make history. In 2009, Maine was the first and only state where — without any previous state court ruling — the legislature passed and the governor signed a bill for equal marriage. In 2012, Maine can be the first and only state where a ballot measure expands state marriage rights.

Taking a look at national public opinion data, it’s clear that gay and lesbian Mainers will be able to marry one day, if only because younger people have different views from their elders.

Gallup 2011 chart on changes in attitudes on inter-racial marriage

Opinions on marriage can change really slowly.

As these Gallup data show, it wasn’t until 1997 that a majority of Americans approved of inter-racial marriage — a full thirty years after the Stupreme Court ruled that bans on inter-racial marriage were unconstitutional.

And shifts in opinions on inter-racial marriage came about both from people changing their views and  because younger people, with more supportive views, replaced older people in the population. Social scientists call this second dynamic “generational replacement.” Gallup found that, while overall 86% in 2011 were fine with inter-racial marriage, only 66% of people over 65 agreed. In contrast, 97% of 18-20 year-olds said it was fine.

And the same dynamic is clear on marriage for gay and lesbian people — but the trend is even faster. Here’s the Gallup data:

2011 Gallup on marriage for gay and lesbian people

Gallup found differences in views by age group, but this 2010 chart from the Pew Research Center really shows them well.

Generational differences in marriage attitudes – Pew, 2010

Although every generational group became more supportive of marriage from when they were first asked about it until recently, there are also really clear differences between the age groups. Older folks are least positive and the youngest ones are most supportive.

Now, does that mean that marriage is going to pass in November?

Well, I don’t like to predict and so, I won’t — certainly not now.

For one thing, while Equality Maine found that 54% support same-sex marriage, a 2010 study of 32 ballot measures (that banned marriage for gay and lesbian people) discovered that, “survey data consistently underestimate voter opposition to legal recognition of same-­sex couples.” (However, the same study also found that the discrepancy between polls and votes has gotten smaller in recent years, so new Maine polls are probably better reflections of people’s views.)

Also, the campaign season hasn’t really gotten started. While Equality Maine has been talking to people about marriage in order to move them to support enabling gay and lesbian people to marry, and these conversations have changed some minds, there will be ads and statements to push those folks the other way.

In 2009, the mobilization and organization for marriage for gay and lesbian people was strong. But those opposed to enabling gay and lesbian people to marriage were also highly activated and motivated. They talked to each other, too, and they voted in large numbers.

Maine is an old state and, as those charts show, older voters are less supportive than younger ones.

On the other hand, in 2009, a lot fewer states allowed gay and lesbian people to marry. More states and countries have it now and it’s much harder to credibly claim that it’s somehow unprecedented or leads to social breakdown.

State and age data on same-sex marriage attitudes, from Lax and Phillips (2009)

And age isn’t everything. Some states have younger populations, but are far less supportive of marriage for gay and lesbian people. An academic paper by Lax and Phillips broke down state public opinion and also looked at age differences.  In a blog post on the chart, they say, “If policy were set by state-by-state majorities of those 65 or older, none would allow same-sex marriage. If policy were set by those under 30, only 12 states would not allow-same-sex marriage.”

Even though Maine has an old population, it is number seven on the Lax and Phillips chart. Today every state above Maine on the chart either has marriage for gay and lesbian people or civil unions, and nearly all of them have marriage.

So it looks like Maine certainly could vote for enabling same-sex couples to marry this fall.

It’s not for sure for 2012, but there’s no doubt that day will come — if not sooner, later.

In the meantime, those on the fence will have to ask themselves why gay and lesbian couples should wait for that day to come. And those supporting marriage for gay and lesbian people should pose the question, politely but directly.

Why shouldn’t every gay and lesbian person be allowed to marry in Maine right now?

Why should they wait for the protections and socially-understood commitment that marriage brings to couples and to families?  Why should they wait to be able to openly refer to their life partners as husband or wife?

It’s going to happen eventually. The only question is WHEN.