Now that the California Supreme Court has upheld Proposition 8's constitutionality, some marriage-equality supporters are ready to begin collecting signatures for a new ballot measure to overturn it in next year's election.

Instead, I hope Californians who support marriage rights for same-sex couples will take a deep, collective breath and engage in levelheaded strategizing about how to achieve the long-range goal of marriage equality.

There are at least two good reasons not to put an anti-Proposition 8 measure on the 2010 ballot.

First, such an initiative has a strong chance of losing. Public opinion about marriage rights for same-sex couples hasn't shifted much since November. In a February Field Poll, for example, fewer than half of California's registered voters said they would support a new ballot measure to legalize same-sex marriage, and about the same percentage would oppose it. These numbers don't bode well for a 2010 ballot campaign to overturn Proposition 8.

Second, win or lose, another Proposition 8 campaign will exact a substantial psychological toll. Research shows that marriage-amendment campaigns have negative mental health effects on the people whose lives they target. A recently published nationwide study, for example, found that during the months leading up to the November 2006 election, psychological distress increased among lesbian, gay and bisexual adults living in states where an anti-gay marriage measure was on the ballot, but not among their counterparts living elsewhere. By Election Day, gay and lesbian residents of the states with anti-gay ballot measures had, on average, significantly higher levels of stress and more symptoms of depression than their neighbors in other states.

Comparable research on the 2008 election isn't yet available, but the limited data I've seen, supplemented by my own observations, leads me to believe the Proposition 8 campaign had a similar, negative effect on many Californians.

It has become almost a cliché to assert that time is on the side of the marriage-equality movement. Younger voters support marriage rights for same-sex couples more strongly than their elders, although not overwhelmingly. That view will eventually achieve majority status in California, perhaps even by 2012. But almost certainly not by next year.

I'm not suggesting that marriage-equality supporters should sit on their hands. There's much work to be done to create a solid majority of California voters who feel they have a personal stake in overturning Proposition 8.

For example, heterosexuals who support marriage rights for same-sex couples can become agents of change by making their opinions known to their spouse, family, neighbors and co-workers.

And it's critically important for lesbian, gay and bisexual Californians to speak directly with their straight relatives and friends about their own experiences, to explain how measures such as Proposition 8 personally affect them. Having such conversations is one of the most potent strategies for changing attitudes. Yet, according to my research, they occur all too infrequently.

Last week's state Supreme Court decision has rightly evoked strong feelings among gay, lesbian and bisexual Californians and their heterosexual supporters. That emotion can be harnessed to build a successful movement for marriage equality in California.

But it shouldn't push us prematurely into a ballot campaign that stands a strong chance not only of losing, but also of ultimately harming many lesbian, gay and bisexual Californians.

Gregory Herek is a professor of psychology at the University of California and has conducted research on anti-gay prejudice for more than 25 years. He helped write amicus briefs submitted by the American Psychological Association for court cases challenging anti-gay-marriage laws in California, Connecticut and other states.