Former Government Minister Pat Carey has admitted people of his generation "do have doubts" about the forthcoming referendum on same-sex marriage - but said they are the greatest supporters when they are convinced.
"This is a campaign like any other - voters need to be asked," he said.
Speaking at the launch of Amnesty International Ireland's campaign for a Yes vote, at the GPO in Dublin, he warned that a Yes result "cannot be taken for granted". However he believes that if passed, it will lead to Ireland becoming "an even more generous, kinder, compassionate, caring and tolerant country".
"People of my generation do have doubts but they are our greatest supporters when they are convinced," he said.
Executive director of Amnesty, Colm O'Gorman, told the 1,000-strong rally that Irish people have a chance to vote for "a Republic of equals".
"Love does not discriminate, and neither should our laws," he said.
Launching the campaign, he said that May 22 will be "an historic date".
"It is a day when we all, as Irish people, have a chance to stand for a republic of equals. A day when we can more fully realise equality for all of our people."
He added it was fitting that they were launching the campaign outside the GPO, where, almost a century ago, those who proclaimed the Irish Republic asserted that Ireland would value and cherish all of its people equally.
Mr O'Gorman said LGBT people should be free to love and commit to each other.