Recently added to the agenda is Doug Mainwaring, a gay activist who opposes same-sex marriage because "denying children parents of both genders at home is an objective evil," he wrote on the website Public Discourse.
Robert Oscar Lopez, who was raised by a lesbian couple and equated child-rearing without a mother and father to abuse, will appear via video — a last minute change due to travel plans.
Erickson said they aren't supporting any particular new bill designed to bolster traditional marriage. State legislative leaders say they are content this session to do nothing, at least until the U.S. Supreme Court weighs in on the constitutionality of Utah's ban.
The rally begins at 7 p.m. inside the Capitol Rotunda. Participants are encouraged to wear pink and blue to show support for hetrosexual marriage.
It's set to begin shortly after another gathering of people on the opposite end of the issue — those who say the state must make same-sex marriage permanently legal.
The Rally for Equality starts at 5 p.m. on the south steps of the Capitol building. Supporters want to end a state appeal to a federal judge's ruling striking down the state's gay marriage ban.
"The message is that we're angry, we're hurting and we're tired of people thinking it's OK to cause pain," said Bob Henline, assistant editor of Q Salt Lake magazine, who organized the rally. "The Legislature needs to say, 'Enough is enough,' and not give the attorney general $2 million to continue this [appeal]."
About 1,000 people have said on Facebook they're attending the event, which will also call for passage of a nondiscrimination law first introduced five years ago.
As the two sides look likely to meet, both stressed civility.
"There are some people who want to express that hurt, they want people to understand that pain, but I really don't want to see this turn into a hate-fest," said Henline.
A donor will send donuts and hot chocolate to the Stand for Marriage rally on behalf of Restore our Humanity, which represented same-sex couples in the Amendment 3 lawsuit.
Erickson said his side is also planning a respectful gathering.
"We believe we can show the world Utah is for marriage, not against anyone," said Erickson. "We simply believe there is something significant about marriage between a man and a woman and want to show that's what Amendment 3 supports."