Mainers United for Marriage’s campaign manager Matt McTighe struck the right note of caution Monday in what was an otherwise enthusiastic rally in support of this year’s same-sex marriage referendum.

No state has ever made marriage equality legal through popular referendum. Many of the same Mainers rallying on the steps of City Hall Monday were also at a somber demonstration on the same spot the day after Election Day in 2009, when Maine voters upheld a people’s veto, taking same-sex marriage off the books.

This promises to be a different campaign held in a presidential election year when turnout is higher. But same-sex marriage supporters should not be lulled into complacency by favorable poll numbers. This will still be a hard fought campaign in which marriage traditionalists will have money and political expertise they will use to frame the issue in their favor.

Opponents have already marshalled some of the old arguments: They cherry-pick verses from Scripture and make claims about nature and the importance of procreation that they would never apply to opposite-sex couples who can’t or won’t have children. They also claim that the state’s failure to impose their religious teachings on others would be a violation of their religious freedom.

But this is not about religion: It is a simple question about whether the law should continue to discriminate against a minority of couples because of who they love. It is a question of whether we will be a society where everyone is treated equally under the law, or one that lets the government continue to reward and punish families based on sexual orientation.

To win this campaign, Mainers United for Marriage and its allies will have to make a voice of reason heard over the din of a highly charged election campaign. And they will have to do more than turn out crowds in Portland, but make sure that their message reaches fair-minded Mainers throughout the state.