Editor's Note: The following essay, released as a public statement and Internet petition, was initially signed by 60 prominent supporters of same-sex marriage rights. Included are six University of Minnesota Law School professors and two Minnesota legislators. Also included are Andrew Sullivan, Jonathan Rauch, Christina Hoff Sommers, Richard Epstein, Charles Murray, Norman Ornstein, Ken Mehlman and Peter Thiel. Find a link to the petition and the full list of signatories here.

The last few years have brought an astonishing moral and political transformation in the American debate over same-sex marriage and gay equality. This has been a triumph not only for LGBT Americans but for the American idea.

But the breakthrough has brought with it rapidly rising expectations among some supporters of gay marriage that the debate should now be over. As one advocate recently put it, "It would be enough for me if those people who are so ignorant or intransigent as to still be anti-gay in 2014 would simply shut up."

The signatories of this statement are grateful to our friends and allies for their enthusiasm. But we are concerned that recent events, including the resignation of the CEO of Mozilla under pressure because of an anti-same-sex-marriage donation he made in 2008, signal an eagerness by some supporters of same-sex marriage to punish rather than to criticize or to persuade those who disagree. We reject that deeply illiberal impulse, which is both wrong in principle and poor as politics.

We support same-sex marriage; many of us have worked for it, in some cases for a large portion of our professional and personal lives. We affirm our unwavering commitment to civic and legal equality, including marriage equality. At the same time, we also affirm our unwavering commitment to the values of the open society and to vigorous public debate — the values that have brought us to the brink of victory.

The gay rights struggle is about freedom and equality for all. The best and most free society is one that allows the largest number to live true to their core beliefs and identities. It is a society that allows its members to speak their minds and shape their own aspirations.

The natural consequence of true liberty is diversity. Unless a society can figure out a way to reach perfect agreement, conflicting views will be inevitable. Any effort to impose conformity, through government or any other means, by punishing the misguided for believing incorrectly will impoverish society intellectually and oppress it politically.

The test of our commitment to liberal principles is not our eagerness to hear ideas we share, but our willingness to consider seriously those we oppose.

There is no evidence that Brendan Eich, the Mozilla CEO who resigned over his $1,000 donation to California's Proposition 8 campaign, believed in or practiced any form of discrimination against Mozilla's LGBT employees. That would be a very different case. He was pressured to leave because of personal political action he took at a time when a majority of the American public shared his view. And while he acknowledged the pain his donation caused, he did not publicly "recant," which some suggested he should have done as the price of keeping his job.

So the issue is cleanly presented: Is opposition to same-sex marriage, by itself, expressed in a political campaign, beyond the pale of tolerable discourse in a free society?

We cannot wish away the objections of Christian, Jewish and Muslim faith traditions, or browbeat them into submission. Even in our constitutional system, persuasion is a minority's first and best strategy. It has served us well and we should not be done with it.

Much of the rhetoric that emerged in the wake of the Eich incident showed a worrisome turn toward intolerance and puritanism among some supporters of gay equality — not in terms of formal legal sanction, to be sure, but in terms of abandonment of the core liberal values of debate and diversity.

Sustaining a liberal society demands a culture that welcomes robust debate, vigorous political advocacy and a decent respect for differing opinions. People must be allowed to be wrong in order to continually test what is right. We should criticize opposing views, not punish or suppress them.

The freedom — not just legal but social — to express even very unpopular views is the engine that propelled the gay rights movement from its birth against almost hopeless odds two generations ago. A culture of free speech created the social space for us to criticize and demolish the arguments against gay marriage and LGBT equality. For us and our advocates to turn against that culture now would be a betrayal of the movement's deepest and most humane values.

We prefer debate that is respectful, but we cannot enforce good manners. We must have the strength to accept that some people think misguidedly and harmfully about us. But we must also acknowledge that disagreement is not, itself, harm or hate.

As a viewpoint, opposition to gay marriage is not a punishable offense. It can be expressed hatefully, but it can also be expressed respectfully. We strongly believe that opposition to same-sex marriage is wrong, but the consequence of holding a wrong opinion should not be the loss of a job. Inflicting such consequences on others is sadly ironic in light of our movement's hard-won victory over a social order in which LGBT people were fired, harassed and socially marginalized for holding unorthodox opinions.

LGBT Americans can and do demand to be treated fairly. But we also recognize that absolute agreement on any issue does not exist. Franklin Kameny, one of America's earliest and greatest gay rights proponents, lost his job in 1957 because he was gay. Just as some now celebrate Eich's departure as simply reflecting market demands, the government justified the firing of gay people because of "the possible embarrassment to, and loss of public confidence in … the Federal civil service." Kameny devoted his life to fighting back. He was both tireless and confrontational in his advocacy of equality, but he never tried to silence or punish his adversaries.

Now that we are entering a new season in the debate that Frank Kameny helped to open, it is important to live up to the standard he set. Like him, we place our confidence in persuasion, not punishment. We believe it is the only truly secure path to equal rights.